GIFT   OF 
WILLIAM  DILLER  MATTHEW 


WILLIAM   DILLER  MATTHEW 


CHIMMOID  FISHES  AND  THEIR 
DEVELOPMENT 


BY 


BASHFORD   DEAN 
PROFESSOR  OF  VERTEBRATE  ZOOLOGY,  COLUMBIA  UNIVERSITY 


WASHINGTON,  D.  C. 

PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 

1906 


CHIM^ROID  FISHES  AND  THEIR 
DEVELOPMENT 


BY 


BASHFORD    DEAN 
o> 

PROFESSOR  OF  VERTEBRATE  ZOOLOGY,  COLUMBIA  UNIVERSITY 


WASHINGTON,  D.  C. 

PUBLISHED  BY  THE  CARNEGIE  INSTITUTION  OF  WASHINGTON 

1906 


EARTH 

SCIENCES 

LIBRARY 


:ARNEGIE  INSTITUTION  OF  WASHINGTON 
PUBLICATION  No.  32 


FROM  THE  PRESS  OF 

THE  WILKENS-SHEIRY   PRINTING  CO. 

WASHINGTON,  0.  C. 


TABLE  OF  CONTENTS. 


Introduction 3 

Paleontological  evidence  as  to  the  position  of  Chimseroids 3 

Anatomical  evidence  as  to  their  position 4-9 

Taxonomy  of  living  forms 6-7 

Collecting  notes 7-10 

Habits  of  Chimsera  colliei;  color,  size,  distribution,  movements.. .     11-18 

Sexual  differences,  food 19-21 

Breeding 23-25 

Mode  of  depositing  eggs 25-27 

Rate  of  embryonic  development 27 

Egg  and  its  capsule 27-40 

General  plan  of  development 41 

Primary  egg  membranes 42-45 

Yolk 45-46 

Germinal  vesicle 47 

Fertilization 48-52 

Segmentation 52-63 

Gastrulation 63-92 

Early  embryos , 75-101 

Late  embryos 102-109 

Comparison  with  other  Chimseroids 109-1 1 1 

"Larval"  Chimsera 111-114 

Organogeny 1 14-132 

Relationships  of  fossil  Chimseroids 133-155 

Summary  of  evidence  bearing  upon  the  position  of  Chimseroids  . .  .  155-156 

Bibliography 159-172 

Description  of  plates 174-194 


ERRATA. 

Page  ii,  for  Regne  read  Regne. 

Page  30,  second  column,  after  Rhinochimaera  pacifica,  for  3  read  33. 

Page  36,  fig.  20,  for  Rhinochimsera  read  Harriotta  (?). 


73464,3 


A  day's  catch  of  Rat-fish,  Chimsera  colliei,  on  the  beach  at  Pacific  Grove 

(near  Monterey),  California.     Beside  the  fish  are  the  float-lines 

and  baskets  with  trawl. 


CHIA/LEROID  FISHES  AND  THEIR  DEVELOPMENT. 

BY  BASHFORD  DEAN, 

Professor  of  Vertebrate  Zoology,  Columbia  University. 


CHIA/LEROID  FISHES  AND  THEIR  DEVELOPMENT. 


INTRODUCTION.      ;    ^  .-*•  •     •;":  ".•/.  : 

Chimaeroid  fishes,  a  group  representing  some  of  the  oldest  and  simplest  of 
backboned  animals,  are  considered  in  the  present  memoir  with  especial  regard  to 
their  relationship  and  descent.  To  this  end,  attention  has  now  been  paid  to  the 
plan  of  their  embryonic  development,  and  upon  this  side  evidence  has  been  obtained 
which,  whether  of  major  or  minor  importance  in  the  study  of  descent,  has  at  least 
the  interest  of  newness.  For  to  the  embryologist  Chimaeroids  have  until  recently 
remained  practically  unknown,  and  they  are  thus  the  only  vertebrate  group  of  their 
anatomical  importance— if  ranked  as  a  subclass — to  have  escaped  investigation. 

On  the  other  hand,  from  the  standpoints  of  comparative  anatomy  and  paleon- 
tology these  shark-like  fishes  have  received  considerable  notice,  and  they  have 
figured  in  publications  of  the  past  half-century  as  the  "most  primitive  vertebrates," 
or,  more  precisely,  as  the  least  modified  descendants  of  the  ancestral  cranium-  and 
jaw-bearing  vertebrate.  And  in  such  a  role  (which  I  now  believe  is  only  partially 
deserved)  they  have  been  given  especial  importance  in  problems  of  descent. 

The  evidence  which  has  been  brought  forward  to  demonstrate  the  primitive 
nature  of  Chimaeroids  is  based  in  part  upon  the  findings  of  paleontology  ;  it  is, 
moreover,  as  one  frankly  admits,  supported  by  anatomical  facts  which  are  broad 
in  range  and  which  have  in  many  instances  been  provided  by  masters  in  morph- 
ology. The  substance  of  this  evidence  is  that  Chimaeroids,  although  shark-like, 
are  nevertheless  widely  distinct  from  the  shark,  and  that  they  represent  a  lower 
plane  in  piscine  evolution.  As  an  aid  to  subsequent  reference,  the  grounds  for  this 
conclusion  may  now  be  summarized. 

PALEONTOLOGICAL. 

Chimaeroids  are  believed  by  some  to  be  older  than  sharks.  Their  fossils,  as 
Walcott  maintains,  occur  among  fragments  of  ' '  fish "  plates  in  the  Ordovician 
(Lower  Silurian)  sandstones.  Sharks,  on  the  other  hand,  do  not  occur — that  is, 
unquestionably — before  the  Upper  Silurian.  Probable  it  is  that  Chimaeroids  lived 
during  the  Lower  Devonian  and,  judging  from  their  dental  plates,  these  forms,  if 
Chimaeroid,  were  highly  differentiated,  even  at  this  early  period.  Moreover,  according 
to  the  studies  of  Jaekel,  paleozoic  Chimaeroids  provide  the  evolutional  stages  from 
certain  archaic  armored  "fishes"  to  the  shagreened  sharks. 


4  CHIM^ROID   FISHES   AND  THEIR   DEVELOPMENT. 

RECENT. 

Many  characteristic  structures  of  living  Chimaeroids  have  been  referred  to  as 
indicating  the  primitive  nature  of  the  group.  The  following  may  be  cited  : 

Dentition  and  dermal  defenses,  by  Jaekel  (1901),  who  maintains  that  the  dental 
plates  are  primitive  or  "statodont,"  i.  c.,  the  ancestral  condition  of  the  "lyodont, " 
or  successional  teeth  of  the  later  sharks.  They  have  thus,  if  I  understand 
Jacket's  view  correctly,  become  greatly  subdivided,  so  as  to  produce  the  cuspid 
teeth  of  sharks.  So, -top,  the  larger  integumental  plates  of  ancient  Chimaeroids 
are  believed  to  have  given  rise  to  cuspid  scales,  and  a  somewhat  similar  view  was 
expressed  by  Pollard  (1891).  According  to  Schauinsland  (1902),  the  scales  of  Callo- 
rhynchus  are  of  so  primitive  a  nature  as  to  be  directly  compared  to  those  of  the 
earliest  Silurian  "sharks."  Finally,  Reis  (1895)  suggests  that  the  curious  unpaired 
tooth  of  mesozoic  Chimaeroids  finds  its  homologue  only  in  the  ancient  Acanthodia. 

Vertebral  column,  with  delicate  ring  "vertebrae,"  characteristic  of  Chimseroids, 
is,  according  to  Schultze  (1817),  but  the  next  stage  above  the  notochordal  con- 
dition of  the  lamprey;  to  Hasse  (1879)  it  represents  a  polyspondylous  condition 
ancestral  to  the  diplospondyly  of  the  simplest  living  sharks;  to  Gegenbaur  (1901) 
"less  differentiated";  to  Howes  (1902)  a  purely  "chordal  type";  to  Meyer  (1886) 
"possibly  primitive";  to  Rabl  (1901)  a  column  which  has  "not  developed  centra." 

Cranium  and  arches. — According  to  Cope  (1870),  the  autostylism  of  Chim- 
aeroids is  in  itself  primitive,  in  spite  of  the  evidence  of  its  secondary  character,  which 
has  been  assumed  on  comparative  anatomical  grounds  from  the  time  of  Johannes 
Miiller  (1838).  So,  too,  Kitchen  Parker  (1883)  inclines,  though  doubtfully,  to  its 
primitive  autostyly;  and  Gadow  (1886)  appears  to  have  a  similar  view  in  stating 
that  dipnoans  were  descended  from  a  "simple  autostylic  form."  The  curious 
labial  cartilages  are  regarded  by  Howes  (1891)  and  others  as  homologous  with  those 
of  hag-fishes.  And  connected  with  these  the  levator  anguli  oris,  according  to  Reis 
(1896),  suggests  closely  the  condition  in  Acanthodian  sharks.  Allis  (1898)  also 
suggests  that  the  jaw  muscle  (adductor)  is  of  a  primitive  type  (i.  e.,  interbranchial), 
and  in  this  he  follows  distinctly  the  more  general  conclusions  of  Vetter  (1878), 
which  are,  indeed,  in  the  latest  time  confirmed  by  K.  Fiirbringer.  The  second 
branchial  arch,  •  it  may  here  be  mentioned,  has  been  referred  to  several  times 
(v.  infra]  as  retaining  archaic  features.  The  labial  cartilages,  furthermore,  are 
said  to  be  primitive,  inasmuch  as  they  represent  the  most  perfect  condition  of 
preoral  gill-arches  known  among  recent  gnathostomes  (K.  Fiirbringer,  1903,  and 
Schauinsland,  1903);  and  a  presymphyseal  cartilaginous  element  is  regarded  as  a 
primitive  copula  between  the  mandibular  and  a  premandibular  arch.  In  fact,  the 
entire  series  of  copulae  is  archaic  (Gegenbaur,  1901). 

Ribs  are  absent,  a  primitive  character,  according  to  Goeppert  (1895). 

Fin  structures  are  of  peculiar  interest.  According  to  Jeffrey  Parker  (1886), 
the  Chimaeroid  is  the  only  vertebrate  to  retain  rudiments  of  a  third  pair  of  limbs.  Its 
paired  limbs  furnish,  according  to  Gegenbaur,  M.  Fiirbringer,  and  Braus,  evidence 
of  the  origin  of  the  paired  limbs  from  gill-arches.  In  this  connection  Howes  (1886) 


EVIDENCE   OF   PRIMITIVE   CHARACTERS.  5 

maintains  that  the  paired  fins  of  Chimaera  are  ancestral  to  those  of  sharks  and 
dipnoans.  Rabl  (1901)  also  refers,  but  in  a  different  aspect,  to  the  primitive  nature 
of  the  fins  of  Chimaera.  By  several  writers  the  unpaired  fins  are  regarded  as 
primitive.  The  fin  spine,  as  Reis  (1896)  maintains,  shows  the  granular  calcification 
of  the  mesozoic  Ischyodus.  The  mixipterygia  are  "of  less  compound  construc- 
tion" (Jungersen,  1898)  than  those  of  sharks. 

Brain,  nerves,  and  sense  organs  have  received  considerable  attention.  Valentin 
(1842)  states  that  in  its  brain  Chimaera  is  intermediate  between  cyclostomes  and 
plagiostomes,  and  his  view  is  shared,  more  or  less  distinctly,  by  Johannes  Muller, 
Mikloucho-Macleay,  Gegenbaur,  Wilder,  and  M.  Fiirbringer.  To  Burckhardt  (i  893) 
the  Chimaeroid  brain  suggests  characters  allied  on  the  one  hand  to  the  primitive 
sharks,  on  the  other  to  the  lower  ganoids,  and  according  to  Studnicka  (1895)  the 
forebrain  is  nearer  the  primitive  form  of  the  selachian  brain  than  even  that  of 
Notidanid.  Jaekel  (1902)  holds  also  that  in  Chimaera,  alone  among  fishes,  there 
appears  an  epiphyseal  opening  in  the  cranial  roof.  In  the  matter  of  cranial  nerves 
Cole  (1896)  states  that  "  Chimaera  is  unrivalled  among  vertebrates,  first,  for  the  ease 
with  which  its  nerves  may  be  dissected  and,  second,  for  the  almost  ideal  results 
that  may  be  attained, "  as  well  as  for  the  peculiarity  of  independent  nerve  roots, 
"archaic  and  perhaps  primitive  in  type."  Similarly,  Fiirbringer  (1897)  comments 
upon  the  peculiar  conditions  of  the  nerves  of  the  occiput.  Collinge  (1896)  notes 
also  the  simplicity  of  the  mucous-canal  system,  which,  he  believes,  separates  widely 
Chimaeroids  and  sharks.  From  the  standpoint  of  the  auditory  organ  Retzius  (1884) 
places  Chimaeroids  in  the  ancestral  line  of  the  modern  elasmobranchs.  Gegenbaur 
(1901),  finally,  notes  that  the  flattened  cord  is  primitive,  like  that  of  cyclostomes. 

Visceral  peculiarities  have  also  been  given  considerable  notice.  Thus  Huxley 
(1872)  refers  to  the  "almost  undeveloped  gastric  division  of  the  alimentary  canal, 
[and]  the  relatively  small  and  simple  heart."  Gegenbaur  (1901)  is  inclined  to  regard 
the  few  turns  of  the  spiral  intestinal  valve  as  the  ancestral  condition  of  the  gut  of 
Lepidosteus  and  Ceratodus.  Leydig(i85i),  followed  by  Mazza  and  Perugia (1894), 
suggests  that  the  many  small  brown  glands  of  the  rectum  represent  the  ancestral 
condition  of  the  digitiform  appendix  of  sharks.  Redeke  (1899)  maintains  that  in  the 
structure  of  the  kidney  Chimaeroids  are  primitive,  since,  among  other  features,  they 
retain  a  remarkable  metamerism  and  have  not  the  modified  Geschlechtsniere  of  sharks. 

The  foregoing  are  the  principal  lines  of  argument  in  favor  of  the  primitive 
position  of  Chimaeroids.  Whether  they  can  be  maintained  in  the  light  of  additional 
evidence,  notably  on  the  side  of  embryology,  is  a  question  which  will  be  discussed 
in  the  present  memoir. 

To  summarize  the  problem  :  Are  the  Chimaeroid  fishes  the  least  modified 
descendants  of  the  primitive  gnathostome?  Or  are  they,  on  the  contrary,  degen- 
erate, specialized,  or  widely  modified?  Are  they,  in  other  words,  close  to  ancestral 
forms  which  gave  rise  to  sharks,  with  which  they  are  obviously  associated — or  are 
they  but  modifications  of  the  shark-like  form?  In  spite  of  the  formidable  list 


CHIM^ROID   FISHES  AND   THEIR   DEVELOPMENT. 


of  citations  as  to  their  phyletic  position,  every  investigator  will  admit  that  Chim- 
aeroids  have  been  but  little  studied — surprisingly  little  studied,  if  we  consider  the 
morphological  problems  which  they  have  trenched  upon  And  in  this  regard  we 
may  safely  conclude  that  the  obstacle  in  the  way  of  the  investigator  has  often 
been  a  simple  one — lack  of  material  for  research.  For,  until  recently,  good  material 
of  Chimsera  was  relatively  rare.  As  a  deep-water  form,  it  was  taken  only  by  special 
fishermen  in  special  localities,  and  even  then,  since  it  was  not  a  food-fish,  it  found  its 
way  rarely  to  a  market  and  still  more  rarely  to  a  laboratory.  This,  then,  has  been 
an  obvious  reason  why  embryological  material  was  not  early  described.  It  may 
finally  be  mentioned  that  fossil  Chimaeroids,  so  important  to  the  general  discussion, 
are  rare,  and,  with  very  few  exceptions,  fragmentary. 

Recent  Chimaeroids  are  included  in  4  genera  and  about  25  species.    An  idea  of 
their  distribution  and  size  may  be  had  by  reference  to  the  following  table : 

TABLE  A.—  Kinds,  Localities,  and  Approximate  Sizes  of  Recent  Chimferoids. 


Genus  and  species. 

Reference. 

IvOcality. 

Size  (±). 

Gronovius,  1754,  Mus.  Ichthyol.,  I,  p.  59, 
plate  iv,  figs,  i  and  2.     Linn.,  as  spe- 
cies,  Syst.  Nat.,   Zoophylae,  ioed.,p. 
236.    (Followed  by  Swainson,  Guiche- 
not,  and  others.) 
Lacepede,  1799,  Hist.  Poiss.,  I,   p.  400, 
plate   xii.       (  Followed    by  Swainson, 
Guichenot,  and  others.  ) 
Hobson  (  1840  ),  Tasmanian  Jour.  Science, 
vol.  i. 
Shaw,  Gen.  Zool.,V,  Pt.  II,  368,  pls.cLVii 
and  CLVIII.      ?  Immature  specimen. 
Dumeril,  1865,  Hist.  Nat.  Poiss.     I.  Elas- 
mobranchs,  694-695.    Immature  speci- 
mens. 

Meters. 
o  .85 

•75 

S  Africa  

.85 
•95 

Richardson,   1841,  Proc.  Zool.  Soc.  and 
Trans.  Zool.  Soc.,  Ill,  174. 
Bory  St.  Vincent,  Diet.  Class.  Hist.  Nat., 
vol.  in,  p.  62,  plate  v. 
Bennett,  Fishes  of  Capt.  Beechey's  Voy- 
age, p.  75,  plate  xxn,  fig.  3. 
Colenso,  1878,  Trans.  N.  Z.  Inst,  vol.  XL, 
pp.  299-300,  plate  xvn. 
Philippi,i892,  An.  Mus.  Nac.  Chile,  Zool., 
p.  ii,  tab.  v,  fig.  i.    Immature  specimen 
(  39  cm.  ). 
Goode  &  Bean  (1894),  Proc.  U.  S.  Nat. 
Mus.,  vol.  xvn,  pp.  471-472. 

(  ?  —  C    milii) 

1.  10 

y 

Chile  

N   Atlantic  

.70 

Garman  (1901),  P.  N.  Eng.  Zool.  Club, 
vol.  i,  ii,  pp.  75-77. 
Mitsukuri    (1895),    Zool.    Mag.    Tokyo, 
vol.  vii,  p.  2. 

Tanan  

1.30 

dicus),  Mem.  M.  C.  Z.,  vol.  xxiv,  pp. 
20-21.     Named  from  egg-case  only. 

*By  any  remote  possibility  could  this  have  been  CallorhyncJtus  centrina,  which  Gronow  described  from  a  speci- 
men which  he  saw  "  in  museo  cl.  Gaubii,  Lugd.  Batav. "  ?  (Syst.,ed.  Gray,  1854,  pp.  15-16.)  His  description  suggests 
Harriotta  rather  than  Rhinochimaera,  since  "habitat  in  Oceano  Americano."  It  is  hardly  conceivable,  however, 
that  Gronow  should  have  happened  across  this  rare  form,  and  from  the  general  vagueness  of  the  description  and 
in  view  of  the  absence  of  the  type  specimen  the  name  CaUorkynchus  centrina  should  be  cast  out  of  the  systematic  list. 


DATA  REGARDING  COLLECTING. 
TABLE  A. — A'l/iifs,  Localities,  and  Approximate  Sizes  of  Recent  Chimccroids — Continued. 


7 


Genus  and  species. 

Reference. 

Locality. 

Size(±). 

Chimaera  

Linnaeus,  Mus.  Regis  Adolph.  Frid.,  vol. 
i,  p.  53.   Syst.  Nat.,  ed.  x,  1758,  vol.  i, 
p.  236. 
Capello(i868),  Jour.  Math.  Phys.  e  Nat. 
Lisb.,  vol.  LV,  p.  314,  plate  HI. 
Gill  (1884),  Proc.  U.  S.  Nat.  Mus.,  vol. 
vi.  p.  254. 
Bennett  (1839),  Fishes,    in-  Zoology  of 
Capt.   Beechey's  Voyage,  p.  71,  plate 

XXIII. 

Gill  (1862),  Proc.  Acad.  Nat.  Sci.  Phila., 
p.  331;  cf.  Dean,   J.  Sci.   Coll.   Tokyo 
(1904),  vol.  xix,  art.  3,  p.  8. 
Waite  (1898),   Ref.  in  "Thetis,"  N.  S. 
Wales  Fisheries,  p.  56. 
Dean    (  1904  ),     Jour,     of    Sci.     College, 
Tokyo,  Japan,  vol.  xix,  art.  3,  pp.  6-9. 
Gunner  (1763),  Det.  Trondhiemske  Sel- 
skabs   Skrifter,   vol.   11,  p.   270,   plates 

V,   VI. 

Ascan.,  Icones  rerum  natur.,  plate  xv.  . 
Gronow  1854,  Syst.,  ed.  Gray,  pp.  16-17.  • 
Shaw,  Gen.    Zool.  ,   vol.  v,  pt.  2,  p.  365, 
plate  157. 
Faber,  Naturgesch.  Fische  Islands,  p.  45. 
Based  on  abnormal  specimens. 
Risso,  1826.   No.  151.   Nat.  Eur.  Merid., 
t.  in,  p.  168. 
Collett,  1904.    Chr.  Videnkabs-Selskabs 
Forh.,  No.  9,  pp.  5-6.   Based  on  young 
specimens. 
Waite   (1899),    Austr.  Museum    Mem., 
IV,  p.  48,  plate  vi. 
Jordan  &  Fowler,  1903,  Proc.  U.  S.  Nat. 
Mus.,  vol.  xxvi,  p.  669  (nee  Jordan  & 
Snyder,   1900,   Proc.  U.  S.  Nat.  Mus., 
vol.  xxin,  p.  338  (  1901)). 
Gill  (  1878),  Bull.  Phil.  Soc.  Washington, 
vol.  ii,  p.  182. 
Gilbert    MS 

Meters. 

(0.70) 

(  ?  —  abbreviata  )  

Pacific  Coast  of  U.  S.. 

.70 

(  =Hydrolagus  colliei  )  .    ... 
(  —  neglecta  )  

.60 

.80 

North     Atlantic     and 
Mediterranean. 
(  ?  Cape    of     Good 
Hope.) 
North  Atlantic 

(  —  Cal.  atlanticus)  

(  —  borealis  )  

North  Atlantic 

(  ?  C.  Bathyalopex)  mirabilis. 

Faroe  

•85 

I.OO 
I.OO 

i-75 
•75 

phantasma  

plumbea  

Hawaii  and  Japan  
Cape  of  Good  Hope.  .  . 

vaillanti  

Dean,   MS.  (type  in  Jardin  des  Plantes, 
No.  2557.) 

(Since  the  above  was  in  type  the  writer  has  seen  in   Japan  two  new  species  of  Chimaera.     These  will  shortly  be 
described  by  Mr.  Tanaka  in  the  Jour.  Sci.  Coll.) 

DATA    REGARDING    COLLECTING. 

It  has  long  been  known  that  Chimaeroids  deposit  large  eggs,  and  that  these 
are  inclosed  in  dart-shaped  capsules,  brown,  heavy,  somewhat  after  the  fashion  of 
sharks,  and  resembling  outwardly  a  frond  of  a  giant  Fucus.  But  further  than  this 
nothing  appears  to  have  been  ascertained  as  to  their  habits  in  breeding.  At  the 
most,  it  was  understood,  from  the  complicated  character  of  the  capsule,  that  the 
eggs  were  carried  in  the  oviducts  for  a  considerable  time. 

This  inference  is  clearly  important  to  one  who  seeks  to  collect  embryonic  stages. 
For,  given  unlimited  time  and  a  locality  yielding  numerous  specimens  of  Chimaera, 
one  could  evidently  secure  gravid  females,  and  from  these  the  requisite  number  of 
mature  egg-capsules.      Thereafter  one  would  have  merely  to  incubate  the  eggs, 


g  CHIM^ROID    FISHES   AND   THEIR   DEVELOPMENT. 

either  in  aquaria  or  in  cases  floating  or  sunken,  and  then,  from  time  to  time,  select 
the  developmental  stages.*  This  mode  of  procedure,  however,  was  not  without  prac- 
tical difficulties,  as  the  present  writer  found  to  his  cost.  In  the  first  place,  he  was 
for  several  years  unable  to  locate  a  region  in  which  Chimsera  could  be  taken  con- 
stantly and  plentifully.  To  this  end  several  points  along  the  European  coast  were 
considered  in  vain.  In  the  bay  of  Naples  Chimsera  is  uncommon,  contrary  to  what 
one  is  led  to  infer  from  the  notes  given  by  Costa  (1854);  for  it  was  found  (1891)  that 
but  few  specimens  could  there  be  obtained,  even  through  the  excellent  collecting 
facilities  offered  by  the  Stazione.  Messina  is  said  to  be  a  favorable  locality,  but 
upon  inquiry  it  was  ascertained  through  Cav.  LoBianco  that  even  there  Chimaera 
was  erratic  in  its  appearance,  and  that  months  might  elapse  before  many  specimens 
could  be  collected.  At  Nice,  also,  inquiry  showed  that  similar  conditions  prevailed. 
The  coast  of  Portugal  gave  the  best  promise  of  abundant  material,  but  the  writer 
found,  during  a  visit  in  1891,  that  collecting  facilities  were  unattainable.  There 
were  still  to  be  considered  the  collecting  possibilities  of  the  coast  of  Norway, 
where,  indeed,  Collett  (1875)  had  already  obtained  an  egg  of  Chimsera,  when  it  was 
learned  that  a  species  of  Chimsera,  C.  colliei,  was  taken  in  considerable  numbers 
on  the  Pacific  coast  of  the  United  States.  It  was  next  ascertained  from  Dr.  Tarle- 
ton  H.  Bean  that  this  form  could  be  taken  in  the  waters  of  Puget  Sound,  and  that 
it  was  especially  abundant  in  the  neighborhood  of  Port  Townsend.  Here,  more- 
over, it  occurred  in  relatively  shallow  water,  and  Dr.  Bean  had  seen  specimens  of 
these  "rat-fish,"  as  they  are  locally  known,  swimming  about  near  the  wharves. 
Puget  Sound  was  accordingly  visited,  Columbia  University  sending  out  a  partyf 
with  a  view  to  collect,  among  other  desiderata,  embryonic  material  of  Chimera  ; 
and  during  a  summer  (1896)  efforts  were  made  to  secure  both  the  eggs  and  the 
living  fish.  The  latter  were  abundant.  About  a  score  of  females  were  examined, 
but  in  no  case  were  eggs  obtained.  From  the  condition  of  the  ovaries  it  was 
inferred  that  the  spawning  season  had  passed. 

Efforts  were  next  made  to  secure  eggs  by  dredging,  but  this  means  also  proved 
in  the  end  fruitless.  It  resulted,  nevertheless,  in  collecting  egg-capsules,  and  in  sev- 
eral localities.  At  one  point  in  Discovery  Bay  as  many  as  sixty  capsules  were  dredged 
(6  fathoms)  during  a  single  morning,  but  these,  as  in  other  instances,  were  found 
to  be  empty.  The  majority  of  the  capsules  were  broken  and  frayed,  and  bore 
evidence  of  having  been  in  the  water  many  months.  Every  effort,  however,  failed 
to  secure  capsules  containing  eggs.  Possibly  they  might  have  been  secured  if 
dredging  in  deeper  water  could  have  bee,n  carried  on,  for  in  no  case  was  material 
obtained  from  deeper  than  10  fathoms.  But  it  was  remarkable  that  so  many 
empty  cases  should  be  taken  close  together,  and  in  shallow  water,  if  they  had  not 


*  Since  these  pages  were  written  Prof.  Schauinsland  has  published  an  extremely  valuable  memoir  on  the  devel- 
opment of  Callorhynchus,  but  he  has  given  no  notes  regarding  the  manner  in  which  eggs  were  secured  at  Chatham 
Island,  or  how  these  embryos  were  reared.  They  appear  to  have  been  collected  separately,  since  he  describes  no 
stage  earlier  than  gastrula. 

fin  this,  as  in  similar  cases,  the  University  was  indebted  to  the  fund  donated  by  Charles  H.  Senff,  Esq. 


DATA   REGARDING   COLLECTING.  g 

been  deposited  in  the  neighborhood.  It  was  still,  of  course,  possible  that  they  had 
been  sifted  into  the  present  position,  perhaps  by  currents,  from  a  greater  depth, 
or  that  the  egg-bearing  capsules  were  actually  close  to  the  empty  ones  and  had 
not  been  dredged.  The  latter  alternative  would  clearly  be  suggested  if  the  eggs, 
like  those  of  certain  species  of  rays,  were  deposited  in  beds,  thrust  into  sand  or 
mud  deeper  than  the  reach  of  the  dredge — a  possibility  which,  a  priori,  seemed 
favored  by  the  dart-like  shape  of  the  Chimseroid  egg-case.  But  even  this  suggestion 
proved  in  the  end  valueless,  for  experiments  showed  that  no  eggs  were  to  be  taken 
by  the  use  of  a  weighted  dredge  (one  which  cut  deep  into  the  muddy  bottom),  even 
when  used  in  the  especial  spot  which  had  yielded  the  greatest  number  of  empty 
capsules. 

The  first  eggs  of  Chimaera  were  obtained  on  the  California  coast  during  the 
latter  part  of  the  same  summer  (1896).  The  writer  is  greatly  indebted  to  President 
Jordan  for  his  invitation  to  visit  the  Hopkins  Marine  Laboratory  at  Monterey,  and 
for  his  suggestion  as  to  the  value  of  the  Chinese  fisher-people  as  zoological  collectors. 
Among  the  fishermen  Ah  Tack  Lee  was  found  to  be  of  the  utmost  service,  skilful, 
persevering,  accurate  in  locating  Chimaera  grounds,  and  keen  in  observing.  He  had 
even  noticed  that  Chimsera  has  the  curious  habit  of  carrying  temporarily  its  pair  of 
eggs  hung  freely  in  the  water  attached  only  by  elastic  threads,  and  that  the  terminal 
filament  of  the  egg-case  is  provided  with  an  end-bulb  which  secures  its  attachment. 

A  few  words  further  regarding  collecting.  During  the  first  summer,  between 
July  22  and  September  12,  there  were  collected  300  males  and  139  females.  Of 
the  latter  1 5  carried  eggs.  Each  gravid  female  was  found  to  contain  two  eggs  in 
practically  the  same  stage  of  development.  The  plan  pursued  was  to  take  those 
eggs  in  which  the  capsule  was  sufficiently  formed  (18  out  of  30  eggs)  and  place  them 
in  a  case,  which  was  then  sunk,  attached  to  a  buoy,  in  water  of  about  30  feet.  Of  the 
number  of  eggs  thus  incubated,  half  were  opened  for  the  earlier  stages;  the  rest, 
unfortunately,  were  lost,  a  storm  having  carried  away  buoy  and  hatching-case.  It 
was  none  the  less  clear,  however,  that  the  method  was  successful,  and  it  was  evi- 
dently but  a  matter  of  time  before  a  fairly  complete  series  of  embryos  could  be 
collected.  A  new  and  stronger  buoy  was  therefore  established  off  the  Chinese 
village,  and  from  that  time  to  the  present,  allowing  always  for  periods  of  laxity, 
the  fisher-people,  influenced  by  Ah  Tack,  have  been  collecting  eggs.  The  only 
practical  difficulty  was  found  to  be  the  suitable  fastening  of  the  hatching-cases,  for 
at  various  times  about  1 50  eggs  have  been  lost. 

The  writer  is  particularly  indebted  to  Dr.  Ray  L.  Wilbur,  of  the  department 
of  physiology  of  Leland  Stanford  University,  for  his  kind  cooperation  in  the  col- 
lecting work.  Dr.  Wilbur  paid  a  number  of  visits  to  Monterey  for  the  purpose 
of  opening  and  preserving  the  eggs,  and  incidentally  prepared  a  number  of  notes 
which  are  referred  to  in  subsequent  pages.  Thanks  to  his  care,  about  a  dozen 
embryos  of  various  stages  were  secured.  There  was  still  lacking,  however,  a  series 
of  segmentation  and  gastrulation  stages,  and  to  obtain  these  the  writer  paid  a 


I0  CHHVUEROID  FISHES  AND  THEIR  DEVELOPMENT. 

second  visit  to  the  Californian  coast  during  the  summer  of  1899.  This  visit  resulted 
in  the  taking  of  179  female  Chimaera,  from  which  20  eggs  were  secured.  In  addition 
to  the  latter,  a  single  egg  containing  a  late  embryo  was  obtained,  which  had  become 
attached  (65  fathoms)  to  one  of  the  hooks  of  a  trawl  line.  It  is  upon  these  stages, 
accordingly,  that  the  writer  has  had  to  depend  for  his  review  of  the  development  of 
Chimsera.  He  may  add  that  he  was  able  to  secure  several  notes  regarding  the 
eggs  of  Chimcera  phantasma  and  of  Chimcera  -mitsukurii  during  a  stay  in  Japan, 
and  that  he  has  further  had  the  opportunity,  thanks  to  his  European  colleagues, 
of  examining  Chima^roid  eggs  and  young  in  several  museums,  notably  in  Paris, 
London,  Berlin,  Bergen,  and  Tromsoe. 

The  present  introduction  would  be  seriously  incomplete  without  reference  to 
the  generous  aid  which  has  been  given  the  writer  at  various  stages  of  his  work. 
Especially  helpful  were  the  suggestions  of  Dr.  Tarleton  H.  Bean  and  President 
Jordan,  and  the  many  courtesies  received  from  Professors  Gilbert  and  Jenkins, 
Directors  of  the  Hopkins  Laboratory,  and  from  other  members  of  the  staff  of  Leland 
Stanford  University,  notably  Professor  Wilbur.  Grateful  acknowledgment  should 
be  made  to  Professor  Theodore  N.  Gill,  who  very  generously  examined  the  proof 
of  the  present  paper.  In  Japan,  also,  while  a  guest  of  the  Imperial  University's 
laboratories,  both  at  Tokyo  and  Misaki,  the  writer  acknowledges  the  valued  aid 
of  Dean  Mitsukuri  and  his  associates.  Finally,  especial  thanks  are  due  to  Dr. 
Naohide  Yatsu,  Rigakushi,  for  his  assistance  both  in  Japan  and  in  New  York, 
preparing  many  text-figures,  and  aiding  notably  in  the  section  of  the  present 
memoir  dealing  with  the  fertilization  of  the  egg.  During  the  latter  study  Mr. 
Yatsu's  comments,  it  need  hardly  be  added,  were  especially  valuable  in  view  of 
similar  studies  which  he  had  undertaken  in  the  case  of  invertebrates. 

The  present  memoir  includes  the  following  themes  : 

I.   Chimsra  and  its  characteristics.     Appearance,  movements,  sexual  differences,  feeding. 

II.  Development: 

Breeding  habits,  mode  of  depositing  eggs,  and  rate  of  embryonic  development. 
The  capsule  and  its  formation. 
The  egg  and  its  membranes. 
Fertilization. 
Segmentation. 
Gastrulation. 

Early  embryos,  i.  <?•,  prior  to  appearance  of  gill-openings. 
Late  embryos,  i.e.,  from  appearance  of  gill-openings  to  time  of  hatching. 
Immature  3roung. 

Morphology.      Reference  to:  (a)  integument  and  dentition;  (£)  skeleton;  (f)  viscera; 
(tf)  nervous  system. 

III.  Fossil  Chimseroids  and  their  significance  in  the  study  of  recent  forms. 

IV.  Chimseroids  in  the  problem  of  vertebrate  descent. 
V.   Literature  of  Chimaeroids. 


I.  CHIM/ERA  AND  ITS  CHARACTERISTICS. 


THE  LIVING  FISH:  COLOR,  SIZE,  DISTRIBUTION,  HABITS. 

This  section  was  suggested  as  a  beginning_fqr  the  present  memoir,  since,  in 
spite  of  many  references,  no  observations  have  hitherto  been  published  describing 
the  living  fish.  In  fact,  the  impression  which  the  rank  and  file  of  zoologists  have  of 
Chimera  is,  I  believe,  derived  from  the  figure*  given  by  Valenciennes  in  the  illus- 
trated edition  of  Cuvier's  Regne  Animal,  which  has  been  copied  trustfully  by  text- 
books, even  by  those  which  have  appeared  during  recent  years.  This  figure  was 
evidently  taken  from  a  stuffed  specimen,  and  gives  the  grotesque  appearance  of  one 
of  Aldrovandus's  monsters,  thus  well  meriting  the  name  of  "Chimsera. "  It  is  a  sur- 


Fig.    I. — Chimaera  colliei.     One- fifth  actual  size. 

The  upper  specimen,  a  male,  shows  the  frontal  clasping  organ  everted,  a  position  which  was  only  retained  by  fastening  the  organ  in 
this  position.  The  mixipterygia  were  turned  somewhat  sideways,  so  as  to  make  them  more  apparent.  The  antero-venlral  clasping  organ 
is  not  conspicuous,  hut  its  lip  is  seen  to  protrude  from  the  vertical  slit  immediately  in  front  of  the  pelvic  fin.  The  figure  indicates  the 
translucency  of  the  snout  region. 

The  lower,  larger  specimen,  a  well-grown  female,  shows  immediately  above  the  base  of  the  ventral  fin  the  tumid  eminence  at  the 
opening  of  an  oviduct.     It  illustrates,  as  secondary  sexual  characters,  the  narrower  pectoral  fin  and  first  dorsal. 
The  photographs  illustrate  the  translucency  of  the  fins  and  delicate  sheen  of  the  newly-caaght  specimens. 

prise,  therefore,  to  find  that  the  fish  is,  in  point  of  fact,  remarkably  beautiful,  its 
contours  well  rounded,  its  fins  delicate,  and  its  colors  almost  herring-like  in  bril- 
liancy. Instead  of '  'Chimsera"  it  deserves  rather  its  popular  Norwegian  name,  '  'king 
of  the  herrings,"  or,  better  still,  its  Japanese  name,  "gin-same"  (silver  shark). 
On  the  other  hand,  it  can  not  be  denied  that  there  is  a  suspicion  of  grotesqueness 

*This  is  scarcely   more  satisfactory  than  the  "fantastic  figures  of   Clusius  and  Aldrovandus,"    to    which    this 
author  refers. 


12 


CHIM^ROID   FISHES   AND  THEIR   DEVELOPMENT. 


in  Chimsera.  In  the  water  the  moving  fish  gives  one  the  impression  that  its  pec- 
toral fins  are  too  large  for  its  body  ;  they  stand  out  prominently,  and  from  their 
transparency  they  remind  one  strongly  of  those  of  some  specialized  teleost,  such  as 
a  gurnet  or  a  flying-fish.  In  figures  (figs,  i  and  2),  reproduced  from  photographs, 
the  transparency  of  the  pectoral  fins  is  indicated,  though  we  gain  little  idea  of  their 
delicacy  and  beauty.  They  are  well  supplied  with  blood,  which  passes  through  the 
transparent  fins  in  delicate  vessels  arranged  parallel  with  the  fin  rays  and  sometimes 
gives  the  fin  a  rosy  tinge. 

COLORS. 

Chimara  collici,  of  which  an  immature  specimen  is  pictured  in  plate  xi,  shows 
lustrous  colors  when  taken  from  the  water.  Its  ground  tone  is  silver,  but  at  every 
movement  it  reflects  metallic  hues — brass,  copper,  and  gold.  Its  snout  is  trans- 


Fig.  2. — Photograph  of  living  Chimaera  colliei. 

This  shows  the  pectoral  fins  extended  on  either  side  of  the  body  at  the  time  of  the  down  stroke  of  the  fin.  The  pelvic  fins  stand  out  on  either 
side  apron-like,  showing  clearly  their  light-colored  anterior  border,  la  this  position  the  spotting  of  the  back  is  conspicuous.  In  lateral  view  (cf.  fig.  I ) 
the  spots  can  scarcely  be  seen. 

lucent,  its  optic  cup  is  luminous,  refracting  pale  greenish-blue,  its  iris  brassy,  and 
on  head  and  trunk  are  tinges  of  rose,  cobalt,  pale-green,  and  madder.  Out  of 
water,  however,  its  brilliant  tones  soon  fade,  and  its  delicate,  scaleless  skin  blotches 
and  dries.  In  the  aquarium,  as  one  could  naturally  expect,  the  fish  fails  to  show 
much  of  its  metallic  luster,  but,  on  the  other  hand,  its  pigments  appear  to  greater 
advantage.  Its  back  region  is  dark  umber,  through  which  pass,  as  the  fish  changes 
position,  shades  of  olive  and  rose-madder.  Its  ventral  region  and  fin  bases  are 
white,  the  fins  themselves  translucent  and  even  transparent.  In  the  adult  the 
paired  fins  show  little  pigment ;  they  stand  out  from  the  body  prominently,  their 
anterior  rims  white,  and  their  constant  movement  adds  greatly  to  the  fish's  beauty. 
It  may  be  added  that  the  dorsal  spine  shows  brightly  in  the  water,  forming  a 


CHIMERA    AND    ITS    CHARACTERISTICS.  ^ 

conspicuous  anterior  rim  to  the  dorsal  fin,  whose  remaining  margin,  in  reality  of  a 
dark  umber,  now  appears  jet-black.  In  side  view  the  body  of  the  fish  exhibits  white 
spots,  but  they  are  not  noticed  in  many  positions.  From  above,  however  (fig.  2),  they 
are  conspicuous,  and  the  general  ground  tone  of  the  fish  appears  much  darker,  a 
change  in  coloration  which  is  probably  of  value  for  protection. 

In  the  matter  of  color  Chimcera  colliei  is  not  far  from  the  mean  of  recent 
Chimseroids  ;  for  some  of  these  have  but  little  pigment,  while  others  are  dusky 
and  even  black.  This  range  in  color  might  be  expressed  in  somewhat  the  following 
way :  With  least  pigment  are  the  Callorhynchids,  with  clear  silvery  sides,  obscured 
only  by  several  large  lateral  blotches,  and  Chimara  phantasma,  with  silvery  sides 
marked  with  longitudinal  dark  stripes.  With  increase  of  pigment  come  the  series 
C.  monstrosa,  C.  affinis,*  C.  colliei,  C.  mitsukurii,  C.  purpiirascens,  and  C.  ogilbyi, 
the  last  almost  entirely  black.  The  distinctly  abyssal  types,  unshaded,  uniformly 
plumbeous,  with  pigmented  lateral  line,  are  Rhinochimaera,  Harriotta,  and  C.plumbea. 

SIZE. 

The  general  relations  of  size  in  Chimseroids  will  be  referred  to  on  a  later  page. 
The  recent  forms  present  a  range  of  length  from  about  60  to  200  cm.  C.  mitsu- 
kurii, even  including  its  long  opisthure,  is  the  smallest  species,  and  the  gradation 
in  size  extends  somewhat  as  follows  through  the  series :  C.  colliei,  C.  affinis,  C. 
monstrosa,  C.  ogilbyi,  and  C.  phantasma;  and  in  the  neighborhood  of  a  meter  in  length 
are  all  other  forms  except  C.  purprtrascens.  Following  the  general  rule  among 
other  fishes,  males  are  smaller  than  females;  in  length  less  by  about  one-twelfth,  and 
in  weight  by  about  one-seventh.  In  this  connection  a  few  comments  may  be  added 
regarding  the  general  shape  of  the  fish.  In  Callorhynchids  and  in  C.  phantasma 
the  modeling  of  the  head,  trunk,  and  tail  is  compact  and  suggests  that  of  Cestra- 
ciont  sharks.  In  general,  males  are  more  slender  than  females.  This  relation  is 
shown  in  fig.  i,  taken  from  a  photograph  of  the  freshly  caught  fish. 

OCCURRENCE,  HABITAT. 

Chimaeroids  are  widely  distributed  (cf.  species  list,  pp.  6,  7).  Callorhynchus, 
however,  is  limited  to  the  south  seas,  and  Chimera  largely  to  the  north.  The 
distribution  of  Chimsera  is  clearly  the  more  general,  for  C.  vaillanti  occurs  at  Cape  of 
Good  Hope  and  C.  ogilbyi  in  Australia.  It  is  the  general  belief  that  all  Chimaeroids 
are  obtained  from  deep  water,  since  the  majority  of  the  species  occur  at  a  greater 
depth  than  the  loo-fathom  line,  while  some  indeed  are  abyssal.  It  is  stated,  for 
example,  that  C.  monstrosa  occurs  in  water  as  deep  as  1,000  fathoms,  C.  affinis^  in 
depths  from  200  to  1,300,  Callorhynchus  up  to  600,  Harriotta  from  700  to  1,000,  and 
Rhinochimsera  at  about  700.  On  the  other  hand,  it  must  be  admitted  that  C. 
colliei  occurs  in  relatively  shallow  water.  Dr.  Bean  records  (Oceanic  Ichthyology, 
p.  32)  that  "it  swims  at  the  surface,"  and  states  further  that  "there  is  no  evidence 


*It  is  probable  that  the  C.  aflinis  recorded  from  great  depths  represents  a  new  species. 
fC.  affinis  is  the  most  abyssal  of  elasmobranchs. 


CHIMJGROID   FISHES  AND  THEIR   DEVELOPMENT. 


that  it  descends  to  very  considerable  depths."  The  writer  has  taken  it  in  water  of 
less  than  5  fathoms  in  Puget  Sound,  and  he  obtained  a  specimen  caught  from 
the  Monterey  wharf  in  water  of  about  3  fathoms.  He  also  secured  over  a  score  of 
immature  specimens  (measuring  about  30  cm.)  from  a  single  haul  of  a  seine  along  a 
shore  reach  near  Port  Townsend,  at  a  depth  not  greater  than  2  fathoms.  It  is 
known,  furthermore,  that  egg-cases  of  this  species  are  plentiful  in  shallow  water. 
C.  -phantasma  and  C.  ogilbyi  also  occur  in  relatively  shallow  water,  /.  e. ,  respectively 
from  10  to  50  and  from  22  to  150  fathoms.  It  appears,  further,  that  Callorhyn- 
chus  is  sometimes  taken  in  water  of  no  great  depth.  (Thus  Plate  records  having 
dredged  off  the  coast  of  Chile  an  egg-capsule  in  water  of  10  fathoms.)  It  follows, 
therefore,  that  in  the  matter  of  vertical  distribution  Chimaeroids  are  not  widely 
different  from  sharks. 


36  ,j  13 

Whistling  Buoy,,     is     15 

K0     .-•  ?-::.'-'-'--'-'."'-i6-. 


BDELLOSTOMA 
GROUND 


27  a 


Fig.  3. — Sketch  of  the  region  of  Monterey,  Cal.,  showing  the  location  of  the  fishing-ground  for  Chimaera. 

Returning  to  the  habitat  of  C.  colliei :  It  can  safely  be  said  that  this  species 
is  more  abundant  in  shallow  water  in  Puget  Sound  than  at  similar  depths  on  the 
California  coast — in  this  regard  paralleling  several  other  fishes  as  well  as  inverte- 
brates. It  is  nevertheless  true  that  in  the  region  of  Monterey  specimens  were  often 
taken  in  water  shallower  than  1 5  fathoms ;  but  experience  demonstrated  that  the 
greatest  number  of  individuals  could  be  fished  in  water  of  60  fathoms.  It  was  also 
found  that  in  somewhat  deeper  water,  60  to  120  fathoms,  females,  although  less 


CHIMERA    AND    ITS    CHARACTERISTICS.  !$ 

abundant,  were  more  apt  to  yield  eggs,  and  that  in  water  of  less  than  40  fathoms 
females  were  usually  eggless.  Collecting  notes  show  that  of  48  females  taken  in  water 
shallower  than  40  fathoms  there  was  but  a  single  specimen  that  yielded  eggs,  and 
in  this  instance  the  egg-capsules  were  quite  immature.  One  concludes,  accordingly, 
that  near  Monterey  this  Chimseroid  occurs  generally  and  at  various  depths,  but  that 
it  is  usually  found  at  the  time  of  spawning  at  a  depth  of  somewhat  over  60  fathoms. 
This  conclusion  is  interestingly  confirmed  by  the  accidental  taking  of  a  naturally 
deposited  egg-capsule  on  a  hook  of  a  trawl-line  in  water  of  65  fathoms. 

The  best  collecting-ground  known  to  the  writer  is  about  3  miles  NNE.  of  Pinos 
buoy,  as  indicated  on  the  map  (fig.  3).  Here  about  500  were  taken,  and  it  is  to 
this  region  that  the  following  notes  apply.  A  trawl-line,*  baited  with  squid  or 
herring,  can  be  laid  in  any  direction  with  a  reasonable  prospect  of  securing  fish;  in 
fact,  rarely  less  than  6  Chimsera  are  taken  in  a  day's  catch;  on  one  memorable 
occasion  7 1  were  taken.  Tabulation  of  results  shows  that  males  are  taken  over  five 
times  as  often  as  females,  f  and  that  of  the  latter  (taken  during  the  summer  months) 
but  i  in  13  bears  eggs  which  can  be  incubated.  It  is  an  interesting  fact  that  in 
trawling  the  fish  are  often  caught  close  together.  The  writer  has  seen  as  many  as 
ten  drawn  into  the  boat  attached  to  adjoining  hooks.  One  infers  from  this  that  the 
line  has  fallen  over  a  restricted  feeding-ground,  where  the  fish  occur  in  great  number. 
And  it  is  found,  furthermore,  that  if  a  fresh  line  is  set  over  the  same  course  more 
fish  are  usually  forthcoming,  and  at  the  same  stretch  of  the  line.  If,  however,  a 
line  is  set  parallel  to  the  first,  and  but  about  200  feet  distant,  one  is  apt  to  find  that 
no  fish  are  taken.  From  the  above  observations  one  may  naturally  conclude  that 
the  especial  feeding-grounds  of  Chimsera  are  sometimes  small  in  size.  Material 
brought  up  by  the  trawl-line  indicates,  further,  that  such  a  favorable  feeding-ground 
is  closely  strewn  with  very  small  rock  fragments.  Where  large  rocks  occur  Chimsera 
is  less  common,  and  it  is  relatively  rare  on  a  sandy  bottom.  There  is  also  evidence 
for  the  belief  that  Chimsera  occurs  in  schools;  and  this  view,  it  may  be  remarked,  is 
prevalent  among  fisher-people  in  widely  separate  localities,  as  in  Lisbon,  Messina, 
Bergen,  Monterey,  and  Misaki. 

Chimsera  is  plentiful  near  Monterey.  According  to  Ah  Tack,  however,  an  even 
more  favorable  fishing-ground  occurs  about  10  miles  to  the  southward,  near  Point 
Lobos,  and  it  is  said  to  be  well  known  to  the  Chinese  fishermen  of  the  neighboring 
Pescaderos.  From  this  neighborhood  eggs  were  collected  during  the  winter  season. 

In  the  region  of  Monterey  the  temperature  of  the  water  during  the  summer 
months  ranges  between  50°  and  60°  F.,  and  the  specific  gravity  is  about  1.028. 

*Six  or  seven  baskets  (/'.  c.,  lines)  were  usually  set,  having  altogether  about  5,000  hooks.  The  boat  employed  was 
a  Chinese  fishing  skiff. 

•(•This  result  agrees  with  the  observations  of  Grieg  and  Olsson  for  Chimicra  monstrosa.  Costa,  on  the  other 
hand,  states  that  in  the  Gulf  of  Naples  no  less  than  14  were  females  out  of  16  specimens  examined  (between  1830  and 
1851),  and  in  Norwegian  waters  Malm  notes  that  26  out  of  33  specimens  were  females. 


i6 


CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 


MOVEMENTS. 

Chimcera  colliei  is  essentially  a  delicate  fish.  When  taken  from  the  water  it 
struggles  but  little  and  soon  dies  (about  15  minutes).  It  makes  no  sound,  save  on 
rare  occasions,  when  it  clicks  its  dental  plates  together  ;  and  it  shows  no  effort  to 
erect  its  dorsal  spine.  In  handling  it  the  fishermen  take  less  account  of  the  formi- 
dable spine  than  of  the  jaws,  which  are  capable  of  inflicting  a  painful  wound,  in  one 
case  snapping  out  at  a  single  stroke  a  bit  of  skin  and  flesh.  It  is  a  difficult  fish  to 
keep  alive,  even  under  favorable  conditions.  In  the  aquarium  of  the  Hopkins  Sta- 
tion it  lived  rarely  longer  than  two  days.* 


Fig.  4. — Chimaera  colliei.     Sketches  of  the  living  fish. 

A.  Swimming  fish  shown  from  in  front.     This  indicates  particularly  the  position  of  the  pectoral  fins ;  from  the  point  marked  with  an  asterisk  (*) 
undulations  arise  which  pass  out  over  the  tip  of  the  fin  as  indicated  by  the  arrows  and  end  at  the  fin's  posterior  margin. 

B.  Fish  shown  in  resting  position.     The  tail  droops  somewhat  and  the  weight  of  the  trunk  is  apt  to  fall  upon  the  fleshy  pad  which  is  present  on 
the  ventral  side  of  the  body  immediately  behind  the  mixipterygia.     The  opening  of  the  operculum  and  the  position  of  the  mouth  in  this,  as  in  the  pre- 
ceding figure,  are  indicated  in  their  normal  position. 

C.  Mouth  region,  showing  the  extent  to  which  the  jaws  open  during  the  process  of  breathing.     As  here  shown,  the  opening  is  even  greater  than 
usual.     Behind  the  mandibular  plates  can  be  seen  the  wide  breathing  valve  b  l',  and  the  prominent  anterior   nostrils.     The  latter  serve  to  pass  water 
lateralward  under  the  large  labial  folds  into  the  mouth. 

The  moving  fish  is  conspicuous  in  the  use  of  its  paired  fins.  The  pectorals  are 
in  constant  motion,  like  delicate  translucent  fansf  moving  to  and  from  the  body, 
and  passing  undulations  one  after  another  along  their  delicate  rims,  somewhat 
as  in  the  pectorals  of  skates.  Thus,  in  the  sketch  given  in  fig.  4  A,  these  fins  are 
seen  in  a  characteristic  position.  They  are  supposed  to  be  moving  dorso-ventrad, 
the  path  of  their  flexible  tips  describing  an  arc  of  about  90°.  At  the  ventralmost 

*Mr.  C.  F.  Holder,  the  director  of  the  aquarium  at  Avalon,  Santa  Catalina  Islands,  informs  the  writer  that  he 
has  been  able  to  keep  C.  colliei  alive  for  a  longer  time,  although  no  definite  time  was  recalled. 

fThe  translucency  of  the  pectoral  fins  is  seen  in  the  photograph  reproduced  in  fig.  i,  page  n. 


CHIMERA   AND    ITS    CHARACTERISTICS.  17 

point  of  their  movement  they  appear  in  the  position  shown  in  fig.  4  B.  A  large  part 
of  the  movement  takes  place  in  the  dermal  web  of  the  fin.  Starting  from  the  point 
marked  with  an  asterisk  (*)  a  wave  of  movement  passes  out  to  the  apex  of  the  fin, 
where  its  greatest  height  is  shown;  then  it  passes  rapidly  around  the  ventral  rim  and 
dies  out  in  the  axil.  This  wave  is  followed  by  another,  more  or  less  rapidly,  accord- 
ing to  the  effort  of  the  fish.  As  the  dermal  rays  are  parallel  to  one  another,  their 
fall  and  rise  suggest  the  movement  of  the  keys  of  a  piano  when  a  finger  is  drawn 
across  the  keyboard.  As  so  much  of  the  conspicuous  movement  is  accomplished 
by  dermal  rays,  the  muscular  bases  of  the  fins  show  to  full  advantage  as  balancing 
organs  (cf.  fig.  2),  almost  as  in  Polypterus.  It  may  be  mentioned,  in  connection  with 
this  constant  movement,  that  the  dermal  margin  of  the  fin  is  so  delicate  that  it  soon 
becomes  ragged  by  wearing  against  the  sides  and  bottom  of  the  tank. 

Chimsera  is  deliberate  in  its  general  movements,  suggesting  somewhat  a  shark, 
but  occasionally  it  shows  great  activity.  On  one  occasion  a  fish  which  had  been 
balancing  quietly  for  some  minutes  suddenly  dashed  about  the  aquarium  and 
then  shot  up  over  the  side.  Quick  movements  of  the  pectoral  fins  greatly  aid  the 
fish's  forward  propulsion;  and  in  the  undulation  of  the  body  the  dorsals  are  far 
more  important  as  swimming  organs  than  the  caudal.  The  ventrals  serve  rather 
passively  as  balancing  organs,  preserving  a  horizontal  plane  and  hanging  behind 
like  an  apron,  their  median  edges  overlapping  (fig.  4  A).  It  may  be  noted  that  the 
mixipterygia,  which  are  so  conspicuous  a  feature  in  museum  specimens,  are  hardlv 
seen  in  the  swimming  fish  (fig.  43).  They  are  neatly  tucked  together  behind  the 
ventral  fins  in  the  median  line  and  can  little  impede  movement.  In  slow  forward 
movement  Chimaera  rocks  somewhat  from  side  to  side,  the  dorsal  fin  functioning 
imperfectly  as  a  keel,  its  spine,  by  the  way,  rarely  more  erect  than  shown  in  the 
figure.  In  resting  the  tail  droops  noticeably*  and  the  fish  balances  by  slow  move- 
ments of  the  pectorals.  The  hinder  trunk  sometimes  rests  on  the  prominent  pad 
of  the  postanal  region.  (PI.  i,  fig.  2,  c.) 

In  further  detail:  The  fish  sometimes  swims  about  freely,  with  a  movement 
described  by  an  observer  as  "butterfly-like,"  from  the  conspicuous  flapping  of  its 
large  pectoral  fins.  It  is  more  active  at  night;  if  placed  in  a  large  tank  it  is  apt 
to  swim  restlessly  from  one  end  of  the  tank  to  the  other.  In  daytime  it  is  quieter, 
and  appears  to  avoid  strong  light.  Occasionally  it  "sails"  or  "flutters"  to  the 
surface,  thrusts  its  snout  out  of  water,  and  then,  suspending  all  movements,  sinks 
to  the  bottom.  Here  it  sometimes  rests,  balanced  on  the  tips  of  its  fins,  like  a 
dipnoan,  or  Squatina,  or  even  a  ray.  In  this  position,  when  otherwise  quiet,  its 
brilliant  eyes  often  show  active  movements.  One  receives  the  impression  that 
captivity  is  irksome  to  the  fish,  an  impression  often  strengthened  by  its  subsequent 
behavior,  for  it  will  suddenly  advance,  then  retreat,  advance  again,  and  sometimes 
thrust  itself  out  of  the  water  in  its  attempt  to  escape. 

*This  condition  has  been  recorded  in  weak,  aquarium-bred  fishes  (e.  g.,  Lepidosteus),  but  in  Chimaera  it  is 
probably  normal,  since  it  was  observed  in  freshly  caught  specimens.  There  is,  nevertheless,  the  possibility  of  its 
being  due  to  change  of  pressure. 


i8 


CHIM/EROID   FISHES   AND  THEIR   DEVELOPMENT. 


B 


C 


G 


The  mode  of  breathing  of  the  fish  is  somewhat 
remarkable.  The  mouth  is  very  small,  and  its  rims  are 
motionless  or  almost  motionless,  scarcely  parted  in  breath- 
ing; so  nearly  closed,  in  fact,  that  the  movement  of 
the  breathing-valve  can  hardly  be  seen.  A  portion, 
probably  a  large  portion,  of  the  water — as  in  the  case 
also  of  dipnoans — is  breathed  through  the  prominent 
nasal  openings  (fig.  4  A  and  c),  whose  cartilaginous  marginal 
flap  is  specialized  to  this  end ;  and  since  the  mouth  is  motion- 
less, it  follows  that  the  branchio-opercular  muscles  are  the 
efficient  means  of  introducing  water  to  the  gills.  In  point 
of  fact,  in  the  living  fish  one  readily  observes  an  extensive 
dilation  and  contraction  of  the  opercular  flaps.  In  spite, 
however,  of  this  extensive  movement,  the  excurrent  open- 
ing is  remarkably  small,  and  at  this  point  the  opercular 
fold  puffs  out  conspicuously,  like  an  opened  valve,  a  small 
one  at  that,  forming  a  slit  about  three-sixteenths  of  an 
inch  in  diameter.  The  rhythmic  opening  and  closing  of 
this  slit  gives  a  further  suggestion  of  its  valvular  nature. 
The  breathing,  moreover,  as  in  the  case  of  other  fishes, 
is  rendered  more  effective  by  the  presence  of  oral  breath- 
ing-valves, operating  so  as  to  close  not  merely  the  open- 
ing of  the  mouth,  but  the  nasal  passage  also.  The  respi- 
ratory movements  are  rapid,  at  least  in  captive  fish.  In 
such  specimens  there  are  counted  as  many  as  100  respi- 
rations a  minute,  a  number  evidently  abnormal.  Occa- 
sionally, when  the  fish  is  swimming,  the  mouth  will  open 
two  or  three  times  spasmodically.  This  occurs  too  rarely, 
however,  to  be  of  especial  respiratory  value  ;  and  it  is 
also  to  be  observed,  if  the  fish  is  a  male,  that  the 
frontal  clasping  spine  will  at  the  same  time  be  elevated 
and  depressed. 

This  correlated  movement  of  clasping  spine  and  jaw 
has  already  been  suggested  by  Reis  on  anatomical  grounds. 
In  this  connection  it  was  once  observed  that  both  mixip- 
terygia  were  suddenly  dropped  from  their  position  close  to 
the  trunk,  rotating  downward  together  from  their  bases, 
their  tips  rotating  through  an  arc  of  90°,  just  as  rigid  fingers 
might  be  bent  downward  from  the  plane  of  the  hand,  but 
no  details  of  this  process  were  seen,  for  they  at  once  rotated  backward  into  their 
closed  position. 


I 


J 


K 


V 5— MandibuUr  dental  plates  of 

Chimaera  colhei,  shown  in  outer  lat- 
eral  aspect,  and  indicating  variation 
in  these  structures.  A  I,  specimens 

from  females ;  j  L,  from  males. 


CHIMERA    AND    ITS    CHARACTERISTICS. 


SEXUAL  DIFFERENCES. 

In  living  specimens  it  is  surprisingly  difficult  to  distinguish  the  sexes  (C  colliei}. 
The  secondary  sexual  characters  of  the  male  are  then  inconspicuous,  and  one  is  apt 
to  identify  it  rather  by  its  smaller  size  and  by  its  slightly  darker  tone.  Breeding 

colors  are  not  marked,  but  at  the  time  of  spawning  the 
female  shows  considerable  color  in  the  anal  and  caudal 
regions,  the  fins  especially  being  suffused  with  blood. 
In  males,  those,  it  appears,  are  in  breeding  colors  in 
which  the  anterior  rim  ~of~  the  pelvic  fins  and  the  ante- 
rior region  of  the  pectoral  fins  are  the  whitest.  It  is 
difficult  to  distinguish  the  claspers.  The  frontal  organ  is 
folded  neatly  away  below  the  surface  of  the  head  ;  the 
mixipterygia  are  closely  apposed  to  the  trunk,  hardly  mod- 
ifying the  contour  of  this  region ;  the  anteropelvic  claspers 
are  tucked  into  their  dermal  pouch,  and  the  mouth  of  the 
pouch  is  nearly  closed.  In  the  female  a  fleshy  pad  lies  in 
the  median  ventral  line  behind  the  pelvic  fins,  and  pro- 
duces a  contour  not  unlike  that  of  the  combined  mixipte- 
rygia. Closer  examination  shows  slight  differences  in  the 
proportions  of  male  and  female;  thus  (cf.  fig.  i)in  the  male 
the  eye  is  relatively  of  larger  size,  the  snout  more  obtuse, 
the  fins  shorter  and  wider,  the  dental  plates  smaller  and 
often  distinguishable  in  shape. 

Dental  plates. — In  C.  colliei  the  mandibular  dental 
plates  of  the  female  do  not  usually  exhibit  as  marked  a 
prong  in  the  "canine"  region  as  the  males.  Nine  such 
plates  are  shown  in  fig.  5  A-I,  sketched  from  jaws  of  adult 
females  selected  at  random,  and  these  may  be  contrasted 
with  the  common  type  of  the  mandibular  plate  of  the  male 
outlined  in  fig.  5  j  and  L.  Great  variation  is,  however, 
apparent  in  both  cases.  Of  the  nine  plates  figured,  four 
(A,  c,  E,  i)  have  no  conspicuous  "canine"  prong,  two  have 
the  prong  well  marked  (D,  c),  the  rest  are  intermediate.  In 
the  males  seven  plates  out  of  ten  were  found  to  be  conspic- 
uous in  the  "canine"  prong,  quite  similar  to  the  specimen 
figured  (j,  L).  One  specimen  (ic)only  was  remarkable  for 
the  evenness  of  its  edge.  Variation  was  also  marked  in  the 
number,  arrangement,  and  distinctness  of  the  tritors,  and 
in  the  general  thickness  of  the  dental  plates.  These  characters,  however,  are  partly 
dependent  upon  the  age  of  the  fish.  In  the  young  the  plates  are  more  delicate 
and  regular,  and  when  viewed  against  the  light  they  are  less  apt  to  show  tritoral 
lines.  When  the  latter  appear  they  are  slender  and  translucent.  In  large  specimens 


D 


Fig.  6. —  Dental  plates  of  Chimaera 


A,  front   view  of    dental  plates  of  large 
specimen  ( female ) . 

B,  dental  plates  of  same  specimen,  viewed 
in  visceral  aspect. 

C,  front   view   of    dental  plates  of    male. 
Observe  especially  the  asymmetry  of  the  right 
mandibular  plate. 

D,  dental  plates  of  same  specimen,  viewed 
in  visceral  aspect. 


20  CHIM^iROID   FISHES  AND   THEIR   DEVELOPMENT. 

the  plates  are  stouter  and  show  irregularly  worn  margins.  In  somewhat  rare  cases 
asymmetry  results.  Two  instances  of  this  kind  are  shown  in  fig.  6.  In  the  first 
(A  and  B)  the  upper  "incisor"  plates  are  quite  different  in  shape  (a  female)  ;  in  the 
second  (a  male,  c  and  D)  the  mandibular  plates  are  irregular,  one  having  the  typical 
"canine"  prong,  the  other  a  fairly  straight  margin.  In  visceral  aspect  one  (D)  car- 
ries the  median  tritors  of  the  palatine  plates  far  forward ;  the  other  (B)  is  prac- 
tically without  a  median  tritor.  In  one  (D)  the  mandibular  plates  form  a  symphyseal 
beak-like  prominence  ;  in  the  symphysis  of  the  other  (B)  there  is  a  noticeable 
notch.  In  general,  there  is  considerable  variation  in  the  number  of  tritors  in  indi- 
viduals of  apparently  the  same  age. 

The  foregoing  peculiarities  are  commented  upon,  since  they  show  that  consider- 
able judgment  is  necessary  to  determine  accurately  species  of  Chimseroids  when 
dental  plates  alone  can  be  studied,  e.  g. ,  in  the  case  of  many  fossil  forms.  Indeed, 
with  so  wide  a  range  of  variation,  it  is  quite  conceivable  that  C.  colliei,  if  known  only 
by  its  dental  plates,  might  be  described  under  several  species,  and  possibly  two 
genera.  The  general  relations  of  the  dental  plates  in  both  living  and  fossil  forms 
are  considered  on  a  later  page. 

FEEDING  AND  FOOD. 

In  view  of  the  special  character  of  the  dentition  of  Chimera,  one  would  nat- 
urally expect  its  food  supply  to  be  definite  in  character.  The  examination  of  the 
contents  of  its  gut,  however,  showed  (C  colliei)  singularly  omnivorous  habits.  It 
is  true  that  the  broken  shells  of  mollusks  are  commonly  found,  as  well  as  fragments 
of  good-sized  crustaceans,  as  indeed  the  scanty  literature  records.  Thus,  in  the  gut 
of  C.  monstrosa  Faber  finds  crustacean  and  shell-fish  fragments ;  Monticelli,  quoting 
Liitken,  Cyprina  islandica;  and  Olsson,  broken  shells  (Leda  and  Venus}  and  bits  of 
large  decapods.  Olsson  finds  also  (and  his  observations  are  the  most  detailed 
hitherto  published  on  the  feeding  of  Chimsera)  chsetopods,  amphipods,  echinoids, 
and  polyps. 

In  C.  colliei  observations  on  about  a  score  of  individuals  showed  a  singular 
mixture  of  foods.  Most  numerous  were  vertebral  columns  of  small  isospondylous 
fishes,  a  few  mollusk  shells,  usually  greatly  crushed,  a  quantity  of  sand  and  fine 
gravel,  squid,  nudibranchs  and  opisthobranchs,  bits  of  cases,  jaws,  and  seta?  of 
annelids,  and  occasionally  a  fragment  of  a  crustacean.  In  one  instance  the  gut  was 
filled  with  seaweed.  One  is  not  surprised,  therefore,  that  this  species  is  taken 
readily  with  various  baits.  In  Puget  Sound  it  is  fished  with  mussel,  clam,  prawn, 
sandworms,  and  even  salt  pork.  At  Monterey  the  greatest  numbers  were  taken 
with  squid;  failing  this,  trawls  were  baited  with  herring,  fresh  or  salted. 

A  curious  feature  in  connection  with  the  feeding  conditions  of  Chimaera  is  that 
in  so  many  specimens  examined  the  gut  is  found  entirely  empty,  even  at  the  time 
the  fish  is  taken  from  the  water.  This  condition  has  been  commented  upon  by 
several  authors,  among  others  by  P.  J.  Van  Beneden  and  Olsson,  the  latter  finding 


CHIMERA   AND   ITS   CHARACTERISTICS.  21 

the  gut  empty  in  as  many  as  5  examples  out  of  16.  The  explanation  of  this  is, 
however,  we  believe,  not  necessarily  due  to  cessation  of  feeding,  for  it  is  found  that 
the  fish  does  not  cease  to  feed  even  while  in  the  act  of  depositing  eggs.  On  the 
other  hand,  from  the  simplicity  of  the  valve  of  the  gut*  it  is  quite  probable,  as 
experiments  on  living  fish  have  convinced  the  writer,  that  the  food  material  is  voided 
between  the  times  of  hooking  the  fish  and  of  drawing  it  into  the  boat. 

Another  curious  feature  connected  with  feeding  is  that  Chimera,  in  spite  of 
the  small  size  of  its  mouth,  can  ingest  objects  of  large  size.  Thus  it  was  found  that 
a  specimen  of  C.  collici  of  moderate  size,  one  whose  mouth  appeared  too  small  to 
admit  a  finger  tip,  had  ingested  a  fish  6  or  7  inches  in  length.  Whether  it  had 
swallowed  it  in  a  single  piece  is  doubtful,  but  judging  from  a  section  of  vertebral 
column,  a  fragment  2  or  3  inches  long  had  been  taken.  Another  specimen  had  swal- 
lowed a  portion  of  a  crab's  carapace  nearly  an  inch  in  length.  Indeed,  the  usual 
baits  taken  measure  over  an  inch  in  diameter,  and  it  is  found  that  they  are  easily 
bolted,  not  cut  or  crushed  by  the  dental  plates.  No  observations  are  recorded  as  to 
the  way  in  which  the  small  and  delicately  shaped  mouth  behaves  while  feeding.  As 
far  as  the  experience  of  the  writer  goes,  a  fish  will  not  feed  in  captivity,  and  it  can 
rarely  be  induced  to  notice  a  bait.  In  one  instance  the  mouth  opened  rather  widely 
and  the  jaws  snapped  together  with  an  audible  click.  It  was  evident,  however,  even 
from  a  single  observation,  that  the  mouth  is  accurately  adjusted  and  can  focus 
its  stroke  with  precision,  somewhat  after  the  fashion  of  the  beak  of  a  bird;  and 
there  can  be  no  doubt  that  the  dental  plates  of  this  species  form  together  a  powerful 
instrument  for  cutting,  rather  than  crushing.  On  one  occasion  the  writer  saw  them 
part  the  line  of  a  trawl. 

In  spite  of  formidable  dentition  and  erectile  dorsal  spine,  Chimaera  is  preyed 
upon  by  other  fish.  According  to  Olsson  it  is  eaten  by  Somniosus  microcephalus ,  and 
small  specimens  have  been  found  in  the  stomach  contents  of  cod. 

*The  stomach  is  broadly  continuous  with  the  intestine  ;  when  food  is  found  it  usually  occurs  in  the  first  turn  of  the 
intestinal  valve. 


II.  DEVELOPMENT. 


BREEDING    HABITS. 

Chim&ra  colliei,  to  which  the  following  notes  refer  unless  otherwise  stated, 
spawns  at  all  seasons  of  the  year.  The  writer  has  himself  collected  eggs  from  June 
till  September.  On  another  occasion  he  received  in  June  a  gathering  of  eggs  which, 
judging  from  their  stages  of  development,  were  deposited  during  March,  April,  and 
May.  In  April  (1898)  Dr.  Wilbur  opened  a  number  of  eggs,  one  of  which  was 
evidently  deposited  in  January  or  late  in  December.  Dr.  Wilbur's  collecting  notes 
remark  further  that  in  December  (1898)  there  was  lost  a  hatching-case  containing 
eggs  (about  two  dozen)  collected  between  September  and  December.  While 
eggs  can  thus  be  secured  throughout  the  year,  a  season  of  maximum  spawning 
probably  occurs.  In  Californian  waters  this  appears  to  be  during  the  late  summer 
and  early  fall. 

The  place  of  spawning  in  this  species  is  known  in  a  general  way.  A  naturally 
deposited  egg  was  taken,  as  above  noted,  in  water  of  65  fathoms  on  gravelly  bottom. 
There  is  good  evidence  that  the  capsules  are  attached  to  rocks  or  heavy  sea-weed, 
since  a  definite  organ  of  attachment  is  present  at  the  filamentous  end  of  the 
egg-case.  It  is  even  possible  that  the  eggs  are  deposited  on  favorite  spawning- 
grounds.  Thus  it  was  found  that  in  an  area  of  about  2  acres  (Discovery  Bay, 
Puget  Sound,  200  yards  off  Tukey's  Point,  in  water  of  6  fathoms)  as  many  as  85 
capsules  were  dredged  in  a  single  day,  while  in  neighboring  regions  they  were  only 
occasionally  noticed. 

From  the  habits  of  Chimera  it  is  very  doubtful  whether  its  copulation  and 
spawning  will  ever  be  observed.  By  indirect  evidence,  however,  the  mode  of 
copulation  appears  to  be  distinct!}'  shark-like.  The  accessory  claspers,  i.  e.,  the 
male's  frontal  spine  and  anterior  appendage  of  the  pelvic  fin,  are  evidently  of  use  in 
securing  the  female  and  retaining  her  in  copulo. 

Garman  long  ago  (1877)  suggested  that  the  frontal  "holder"  functioned  in 
securing  the  pectoral  fin  of  the  female  and  in  "turning  her,"  thus  serving  like  the 
hooks  on  the  pectoral  fins  of  the  male  ray;  and  he  further  maintained  that  the  pelvic 
claspers  were  used  for  holding  the  mixipterygia  when  erected.  As  far  as  the  frontal 
spine  is  concerned,  a  more  probable  interpretation  is  that  the  male  Chimera  (cf. 
the  position  in  shark)  wraps  its  body  about  the  female  and  secures  final  attachment 
in  copulo  by  attaching  the  spine  near  the  female's  dorsal  fin ;  for  it  was  found,  in  an 
examination  of  specimens  which  were  about  to  deposit  eggs,  that  well-marked  scars 
were  present,  indicating  the  point  of  attachment.  The  region  of  the  dorsal  fin  in  such 
examples  is  shown  in  figs.  7  to  1 1 ;  and  there  can  be  no  question,  from  a  closer 
examination  of  the  scars,  each  of  which  is  shown  enlarged  on  the  same  page 

23 


24 


CHIM/EROID   FISHES  AND  THEIR  DEVELOPMENT. 


according  to  corresponding  numbers,  that  these  were  caused  by  the  frontal  organ, 
for  each  shows  a  number  of  small  punctures,  usually  8  to  12,  corresponding  in 
arrangement  to  the  cusps  of  the  frontal  spine,  as  one  may  demonstrate  by  experi- 


12 


,/ 


f 


10 


10 


,11 


Figs.  7  to  1 1. — Region  of  dorsal  fin  in  (emale  specimens  of  Chimaera  colliei,  showing  marks  of  frontal  clasping  organ  of  male.  The 
smaller  numbers,  i  to  14,  and  (at  the  left)  enlargements  with  corresponding  numbers,  show  positions  and  details  of  scars  made  by  frontal 
clasping  organ. 

ments  with  the  spine  itself.  The  majority  of  these  scars  occur,  moreover,  in  the 
position  where  they  would  be  expected  if  the  male  assumed  in  copulo  the  same 
position  as  the  shark.  With  few  exceptions  they  are  situated  in  the  region  of  the 


BREEDING  HABITS.  25 

first  dorsal  fin.  In  some  instances  the  presence  of  several  scars  indicates  that  a 
number  of  attachments  were  attempted.  The  most  posterior  scars  (figs.  10  and  1 1, 
scars  13  and  14)  are  rather  scratches  than  points  of  attachment.  In  spite  of  this 
evidence,  however,  the  writer  must  remark  that  one  gravid  specimen  examined 
failed  to  show  a  scar  in  the  region  referred  to.  On  the  other  hand,  there  was  little 
doubt  that  the  marks  referred  to  were  made  on  the  fish  prior  to  capture,  and  that 
in  those  specimens  no  other  marks  were  noticeable. 

The  antero-pelvic  clasping  organs  are  distinctly  erectile  and  probably  serve  as 
an  additional  means  of  attachment  in  copula.  Thcycan  hardly  function  as  Garman 
has  indicated  (i.  e. ,  to  hold  the  erected  mixipterygia),  if  for  no  other  reason  than 
that  if  thus  held  the  mixipterygia  not  only  diverge  widely,  but  are  so  closely 
fastened  to  the  side  of  the  male  that  they  can  not  well  be  made  to  enter  an  oviducal 
opening. 

It  may  be  noted  that  Parker  (1897)  states  that  spermatophores  are  present  in 
Callorhynchus.* 

MODE  OF  DEPOSITING  EGGS. 

Two  eggs  are  deposited  almost  simultaneously;  and  it  is  more  than  probable 
that,  just  as  in  sharks,  considerable  time  is  taken  in  the  actual  process  of  extruding  the 
eggs.  In  fig.  12  is  shown  the  anal  region  of  a  specimen  (C  phantasma)  in  which  the 
egg-capsules  were  protruding.  This  specimen,  it  may  be  said,  had  been  rather 
carelessly  handled  and  had  been  in  the  well  of  a  fishing-boat  nearly  half  a  day,  but 
the  eggs  showed  no  tendency  to  become  detached.  The  capsules  in  this  instance 
are  still  deeply  inserted  in  the  oviducts;  even  at  a  later  stage  they  remain  firmly 
attached.  In  the  condition  shown  in  plate  i,  fig.  4,  the  capsules  protruded  as  far 
as  the  base  of  their  terminal  filament,  yet  they  remained  attached  to  the  fish  for 
several  hours  and  were  thus  brought  to  the  Hopkins  laboratory.  It  was  then  found, 
as  the  figure  indicates,  that  the  terminal  filament  passed  throughout  the  length  of 
the  thickened  portion  of  the  oviduct  and  terminated  in  an  expanded  tract  in  the 
crease  at  the  lower  end  of  the  capsular  gland.  At  this  stage  the  walls  of  the  lower 
oviducts  were  contracted  and  embraced  tightly  the  capsular  filament.  At  a  still 
later  stage  the  filament  hardens  into  a  dark-colored  string,  and  the  capsules  then 
hang  freely  into  the  water,  2  or  3  inches  distant  from  the  body.f  Such  a  condition 
was  once  observed  by  the  writer,  and  he  found  that  even  thus  the  eggs  were  firmly 
attached.  In  removing  them  the  connecting  strings  were  observed  to  possess  con- 
siderable elasticity.  They  could  even  be  lengthened  and  shortened  several  inches. 
When  detached  from  the  fish  they  showed  that  the  terminal  was  still  immature, 
soft,  and  pale  in  color.  It  is  to  be  regretted  that  in  this  specimen  no  dissection  of 

*Doubt  has  been  expressed  as  to  the  presence  of  a  receptaculum  seminis.  (Hyrtl  in  Sb.  Akad. ,  Wien,  1853,  XI, 
pp.  1078-1087,  and  Redecke,  Tydschr.  d.  nederl.  Dierkund.  Ver,  zd  ser.,  Decl.  vi,  1899,  p.  125.)  In  this  connection 
ff.  Howes  as  to  a  "rudiraental  vesicula  seminis"  in  Chimaera  ( ? ).  (J.  Linn.  Soc.,  vol.  xxm,  p.  405.) 

fProf.  Einar  Lonnberg,  in  a  recent  letter,  which  I  am  permitted  to  quote,  states  that  he  has  observed  (in  July, 
1898,  in  the  market  of  Bergen),  a  specimen  of  Chimcera  monstrosa  in  which  egg-capsules  were  protruding  from 
the  oviducts,  somewhat  in  the  condition  shown  in  the  present  fig.  12. 


26 


CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 


the  oviducts  was  made,  for  the  filaments  were  so  perfectly  formed  that  they  might 
well  have  yielded  some  interesting  notes  as  to  their  terminal.  That  this  is  finally 
a  bulbous  organ  there  can  now  be  no  doubt.  Ah  Tack  early  made  a  drawing 
of  it,  but  the  writer's  skepticism*  continued  until  word  was  received  from  Dr. 
Wilbur  (May  i,  1899)  that  he  had  himself  seen  the  terminal  organ,  describing  it 
as  a  "sort  of  disc,"  and  figuring  it  (plate  i,  fig.  3)  very  much  as  Ah  Tack  had 
done.f  From  all  this  it  follows  that  the  ovulation  of  this  Chimseroid  is  highly 
specialized.  The  elaborate  egg-case  is  not  shot  out  quickly  nor  festooned  on  fixed 
objects  by  its  terminal  filament,  as  in  the  case  of  recent  selachians,  but  is  carried 


Fig.  12. — Region  of  ventral  fins  ol  a  specimen  of  Chimera  phantasms,  in  which  egg-capsules  protruded  from  oviducts.  This 
specimen  was  taken  (Misalci,  Japan)  in  water  of  about  1 50  fathoms  and  shows  the  intestine  everted,  a  condition  usual  in  a  fish 
taken  from  such  a  depth. 

about  for  a  longer  time,  protruding  from  the  oviducts  before  it  is  made  fast  to  a 
suitable  object.  This  is  possibly  a  stone,  %  and  if  the  eggs  are  thus  attached  near 
or  among  rock  masses,  we  have  a  suggestion  why  embryo-bearing  capsules  have 
never  been  dredged. 

"Pains  were  taken  to  observe  the  process  of  depositing  the  eggs.  To  this  end  a  fish  was  secured  in  which  egg- 
capsules  were  just  protruding.  This  specimen  was  closely  watched,  but  succeeded,  nevertheless,  in  depositing  the  eggs 
unobserved.  The  process  could  not  have  taken  more  than  10  minutes.  The  capsules  were  immature,  possessing 
scarcely  more  than  a  stump  of  the  filament  (plate  n,  fig.  10). 

fUnfortunately  this  capsule  was  lost  in  a  hatching-case  swept  away  by  a  storm. 

|Ah  Tack  states  that  several  times  his  trawl  lines  have  brought  to  the  surface  capsules  which  still  retained  small 
stones  attached  to  the  terminal  organ  of  the  filament. 


DEVELOPMENT. 


It  is  observed  that  after  the  eggs  are  deposited  the  oviducal  openings  are  everted, 
tumid,  suffused  with  blood  (plate  i,  fig.  2;  cf.  also  Costa,  p.  23,  plate  n,  andGaimard, 
plate  xx,  in  Voy.  en  Islande  et  au  Groenland);  in  fact,  the  entire  anal  region  is 
bloodshot,  including  the  fin  margins. 

In  many  instances  (August  and  September)  the  fish  may  soon  spawn  again. 
This  is  evident  from  the  mature  condition  of  a  pair  of  ovarian  eggs  which  were 
found  in  specimens  having  tumid  oviducal  openings. 

RATE  OF  EMBRYONIC  DEVELOPMENT. 

The  young  Chimaera  spends  the  greater  part  of  a  year  in  its  capsule,  probably 
not  less  than  nine  months,  and  possibly  as  long  as  twelve.  The  duration  of  the 
younger  stages  is  known  with  reasonable  accuracy.  In  the  following  table,  show- 
ing the  rate  of  development  of  C.  colliet,  the  results  are  based  upon  eggs  in  hatch- 
ing-cases (water  temperature  between  50°  and  60°  F.). 

TABLE  B. — Kate  of  Embryonic  Development. 


Stage. 


Fertilization. 
Cleavage. . 

First. . . 

Second . 

Sixth... 

Blastula  

Gastrula  .. 


Embryo. 


Estimated 

duration  of 

entire  process. 


36  to  60   hours 
3  days. 


4  days . 
14  days . 


Approximate  age  of  specimen  in  material  studied,  time  of 
fertilization  included.* 


2  days  3  hours. 

2  days  5  hours. 

3  days. 

5  to  9  days. 

10  days. 

12  days,  corresponding  to  Balfour's  shark  embryo  stage  C. 

19  days,  corresponding  to  Balfour's  shark  embryo  stage  D. 

21  days,  corresponding  to  Balfour's  shark  embryo  stage  E. 

24  days,  corresponding  to  Balfour's  shark  embryo  stage  F. 

28  days,  corresponding  to  Balfour's  shark  embryo  stage  G. 

33  days,  corresponding  to  Balfour's  shark  embryo  stage  I. 

90  days,  f  corresponding  to  Balfour's  shark  embryo  stage  L. 
130  days,  f  corresponding  to  Balfour's  shark  embryo  stage  N. 
180  days,  \  corresponding  to  Balfour's  shark  embryo  stage  O. 


*A  re-examination  of  the  writer's  collecting  notes  leads  him  to  estimate  that  fertilization  takes  place 
in  about  two  days.     This  time  has  therefore  been  added  in  assigning  ages  to  the  various  stages. 

tThese  figures  are  based  upon  notes  given  by  the  fishermau  Ah  Tack,  recording  months  when  eggs  were 
placed  in  the  hatching-cases.  If  these  are  accurate,  and  I  believe  they  are  reasonably  so,  Chimoera  does  not 
differ  notably  from  a  shark  in  its  rate  of  later  embryonic  growth. 

THE  EGG. 

The  egg  of  C.  colliei  measures  in  its  capsule  about  2.9  by  1.9  by  1.3  cm. 
(average).  It  is  inclosed  in  a  delicate  vitellina;  when  this  is  ruptured,  the  egg  breaks 
into  a  syrupy  mass,  very  much  as  the  egg  of  a  typical  selachian.  Especially 
soft  is  the  egg  about  the  time  of  its  passage  into  the  oviduct.  At  such  a  stage 


28 


CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 


(plate  n,  fig.  5),  if  placed  on  a  flat  surface,  it  spreads  out  circu- 
larly, measuring  in  this  way  over  5  cm.  in  diameter.  It  is  pinkish 
(it  is  earlier  yellow,  and  later  creamy  white),  although  its  tint 
is  probably  due  to  the  capillaries  in  the  enveloping  membrane. 
These  capillaries,  it  may  be  noted  in  passing,  become  focused 
around  a  well-marked  stigma. 

In  the  disposition  of  yolk  the  egg  differs  slightly  from  that  of 
typical  selachians  (e.  g.,  as  shown  by  Riickert  in  Torpedo).  (Cf. 
p.  47.)  In  the  matter  of  fertilization,  sperms  have  been  found  in 
the  uppermost  portion  of  the  oviduct,  and  there  can  be  little  ques- 
tion that  the  earliest  stages  of  fertilization  here  take  place.  It  is 
further  evident  that  the  eggs  are  received  in  the  oviducts  one  after 
another,  for  there  is  but  a  single  funnel  present,  and  it  is  prob- 
able, from  the  condition  of  the  ovaries  examined,  that  the  eggs 
are  shed  from  both  right  and  left  sides  at  almost  the  same  time. 
By  this  inference  we  can  also  best  explain  the  passage  of  the 
eggs,  one  to  the  right  oviduct  and  one  to  the  left,  since  if  the  first 
egg  were  blocking  the  upper  portion  of  one  oviduct,  the  second 
egg  would  naturally  pass  to  the  other.  The  fluidity  of  the  egg 
at  this  stage  unquestionably  aids  it  in  passing  through  the  narrow 
opening  of  the  oviduct  in  the  zone  of  the  capsular  gland  (plate  n, 
fig.  6),  granting  even  that  this  opening  is  greatly  enlarged  at  the 
time  of  the  egg's  descent 

THE  EGG-CAPSULE. 

The  egg-capsules  of  Chimseroids*  are  illustrated  in  figs. 
13-23,  and  a  list  of  those  hitherto  described,  together  with  notes 
as  to  the  depth  at  which  they  were  collected,  is  given  in  Table  C 
on  page  29. 

An  examination  of  the  capsules  indicates  that  they  may  be 
grouped  according  to  the  genera  and  species  which  they  repre- 


Fig.  1 3. — Spirangium  (egg- 
capsule  of  Chimaeroid?). 
From  lithographic  stone 
of  Lerida  (Spain).  Ju- 
rassic. After  Sauvage. 


*In  the  instance  of  C.  colliei,  the  parts  of  the  young  fish  are  found  to  have  a  definite  relation  to  the  egg-capsule, 
and  these  relations  are  probably  constant  in  other  Chimaeroids.  The  capsule  may  therefore  be  referred  to  as  containing 
a  case  for  the  embryo,  which  is  always  subdivided  into  snout  sheath,  trunk  sheath,  and  tail  sheath.  The  case  has 
also  a  dorsal  side,  which  bears  anteriorly  an  opercular  flap,  which  provides  for  the  ultimate  escape  of  the  young,  and 
a  ventral  side,  which  is  (usually)  the  more  convex.  Other  descriptive  terms  are:  Lateral  zuebs,  which  are  flanges  of  the 
capsule  extending  outward  from  the  case.  These  are  sometimes  strengthened  transversely  by  stout  undulating  thick- 
enings, rugfe,  of  the  web;  and  these  often  pass  over  into,  or  are  .associated  with,  more  delicate  and  more  numerous 
distal  rugulce,  or  both  rugae  and  rugulae  may  become  close-set,  rib-like  thickenings  passing  from  case  to  web  margin, 
costie  ;  these  terms  will  be  found  useful  in  description.  Opercular  ridges,  overlapping,  form  together  the  rims  of  the 
opercular  flap.  In  their  specialization  these  rims  have  sometimes  protruding  serrulcc,  which  interlock  and  form  a  close- 
set  grating,  which  admits  water  for  the  respiration  of  the  embryo  and  which  later  breaks  open  to  permit  the  young  fish 
to  escape  from  the  capsule.  These  grating-like  fenestrulae  are  collectively  homologous  with  the  (pair  or  several  pairs  of) 
lateral  slits  which  appear  near  the  rims  of  the  egg-capsule  of  the  shark  or  ray.  Continuing  the  line  of  the  fenestrulae, 
ventilating  apertures  are  also  present  at  the  sides  of  the  tail-sheath,  and  these  may  be  termed  caudal  fores.  They  are 
typically  furnished  with  "tongue-bars,"  which  double  the  number  of  simple  openings.  A  dorsal  keel  is  present  in  the 
capsules  of  Chimaera. 


THE   EGG-CAPSULE. 


sent.     In  further  detail,  the  capsules  may  be  classified  on  somewhat  the  basis  shown 
by  Table  E  on  page  30.     (Cf.  this  table  for  proportional  measurements.) 

TABLE  C. — Egg-Capsules  of  Chimceroids. 


Approximate 
depth  at  which 
deposited. 

Species. 

Reference. 
(For  detailed  reference 
c/.  Literature  List  .  ) 

Fathoms. 

10-f 

Callorhynchus*  

1842     Miiller,  J. 

1865   "THrmeril,  A 

1871     Cunningham,  R.  O. 

1880     Gunther,  A. 

1897     Parker  and  Haswell. 

1899     Garman,  S. 

1901     Vavra. 

^  to  6^ 

1901     Jaekel,  O. 
1903     Dean,  Bashford. 

J       HJ     \JJ 

?3OO 

mitsukurii                      

1904     Dean,  Bashford. 

•  j""* 

?2OO 

monstrosa                        .... 

1855     Nilsson,  S. 

1858     Lutken,  C.  F. 

1874     Collett,  R. 

1877     Malm,  A.  W. 

1889     Gunther,  A. 

1892     Alcock,  A.  (C.  monstrosa?). 

1896) 
and  >  Grieg,  J.  A. 
1899) 

1896     Olsson,  P. 

phantasma  

1901     Jaekel,  O. 
1889     Gunther,  A. 

ISO 

375 

Harriotta  raleighana  

1904     Dean,  Bashford. 
(v.  infra) 

3  1  J 
3OO-6OO 

Rhinochiniasra  pacifica  

1904     Dean,  Bashford. 

c6i 

indica  

1891     Wood  Mason,  J.,  and  Alcock,  A. 

j 

*Referenceis  made  in  the  present  paper  (pp.  30,  et  scq.  and  figs.  15  B-F)  to  several  "species"  of  capsules 
of  Cattorhynchus ;  e.  g.,  Specimen  7983,  Zool.  Mus.  Jardin  des  Plantes,  Cape  of  Good  Hope  (Quoy  and 
Gaimard);  Specimen  7982,  Zool.  Mus.  Jardin  des  Plantes,  Cape  of  Good  Hope  (Voyage  Peron); 
Specimen  7984,  Zool.  Mus.  Jardin  des  Plantes,  Chile  (Martinez)  ;  Specimen  8823  A,  Zool.  Mus.  Jardin  des 
Plantes,  Straits  of  Magellan  (Savatier).  Also  to  specimens  from  Australia  in  the  British  Museum. 

TABLE  D. — Egg-Capsules  of  Fossil  Chimceroids. 


fschyodus  (  =  Alclodus) fcrrugineus : 
(Upper  Jurassic)  1901,  Jaekel,  O. 

The  fossils  Spirangium,  Palasoxyris,  Fayolia,  and  similar  forms  may  prove  to  be  the  egg- 
capsules  of  Chimseroids  or  of  cestraciont  sharks.     From  their  imperfect  preservation, 
however,  they  may  equally  well  be  coprolites  of  fishes  having  spiral  intestinal  valves.   To 
a  somewhat  more  definite  category,  however,  belongs  the  following  "Spirangium"  : 
Spirangium: 

1903,  Sauvage,  H.  E. 

Cf.  fig.  13.     If  this  prove  to  be  a  Chimaeroid  egg-capsule  it  is  remarkable  in  a  feature  suggest- 
ing the  capsule  of  a  cestraciont — marginal  webs  arranged  in  spiral. 


CHIMJEROID  FISHES  AND  THEIR  DEVELOPMENT. 

TASL*  E. — £gf-Cmses  of  Otimaroids  Compared.     (Cf.  figs.  13-16.) 


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THE   EGG-CAPSULE. 


CLASSIFICATION  OF  CAFSVLES. 


Fig.  14.     Egg-capsulr  oj  lossil  Chimirroid,  I«chyoA»(AI*«odu»), 
from  Dogger  bcd$  (Jurassic),  Germany.    Alter  Jaekcl.    Actual 


From  the  materials  provided  in  the 
present  table  and  figures  the  egg-capsules 
of  Chimaeroids  may  be  classified  on  some- 
what the  following  basis : 

Callorhynchus.    (Fig.  15  A-F.) 

Capsules  with  case  spindle-shaped;  snout-sheath 
subequal  in  length  to  the  tail-sheath;  lateral  web 
broad,  exhibiting  stout  rugae;  of  these  a  conspicu- 
ous pair  proceeds  outward  from  hinge  of  opercular 
valve.  No  serrulse  present,  the  opercular  ridges 
merely  separating  to  admit  water,  as  in  related 
structures  in  sharks.  No  caudal  pores;  in  their 
place  a  slit  on  each  side  of  tail-sheath  opening  on 
the  ventral  side  in  the  angle  between  web  and  case. 
Anterior  lip  of  operculum  transverse,  situated  on 
dorsal  side  at  a  considerable  distance  from  anterior 
margin  of  capsule.  No  dorsal  keel.  Heavy  cap 
sules,  leathery  and  glabrous. 

No  capsules  of  Callorhynchus  are 
known  to  be  definitely  associated  with  par- 
ticular species,  although  many  of  the  speci- 
mens preserved  in  museums  are  ascribed 
to  "  C.  MAmtftec."  From  a  study  of 
the  capsules  of  the  species  of  Chimaera,  * 
however,  it  is  clear  that  the  differences 
between  the  capsules  described  are  such 
that  we  can  not  believe  that  they  belonged 
to  the  same  species.  Thus  the  Chilean 
capsule  (fig.  15),  described  by  Jaekel  as 
"Ca/.  ariJarf/ictis"  (a  synonym  of  C,  caJ- 
lorhynthHS  of  Valenciennes)  is  probably  of 
a  different  species  from  the  similar  egg- 
case  (fig.  1 5  A)  figured  by  Dumeril,  and 
this  in  turn  is  notably  different  from  sev- 
eral specimens  in  the  zoological  museum  of 
the  Jardin  des  Plantes,  which  the  writer 
was  recently  permitted  to  examine  through 
the  courtesy  of  Professor  Yaillant.  The 
latter  capsules  are  accordingly  figured 


*  Variation  of  the  capsules  within  the  range  of  the  species  was  studied  by  the  writer  in  the  instance  of  Ckima-ra 
About  eighty   capsules  were  examined,  but  the  variations  were   found   different  in   character   from   those 
referred  to  in  the  present  pages. 


CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 


(fig.  1 5  B-F)  from  tracings  of  the  specimens,  and  they  will  be  seen  to  present  a 
considerable  range,  both  in  proportional  measurements  and  in  the  number  and 
character  of  the  rugse  and  rugulse. 


Fig.  1 5.— Egg-capsule  of  Callorhynchus.     From  specimen  collected  in  Chile  by  Plate.     After  Jaekel.     Actual  size. 
Fig.  1 5A. — Egg-capsule  of  Callorhynchus.  Locality  unknown.     After  Dumeril.     About  two-thirds  actual  size. 

In  further  detail,  the  capsule,  fig.  153  (Cape  of  Good  Hope),  resembles  most 
closely  that  of  fig.  1 5  E  (Magellan).  It  differs,  on  the  other  hand,  in  having  the  walls 
of  the  case  more  delicate  and  transparent,  in  spite  of  the  fact  that  the  Magellan  speci- 


THE    EGG-CAPSULE. 


33 


men  (or  specimens)  is  much  smaller  in  size.  This  difference,  therefore,  could  hardly 
prove  a  matter  merely  of  age.  Another  capsule  (Chilean),  fig.  150,  is  again  quite 
unlike  the  specimen  figured  by  Jaekel.  It  is  almost  a  third  larger  in  size,  but  nar- 


\ 


Fig.  15  B. — Egg-capsule  of  Callorhynchus.     (Quoy  and  Caimard.)    From  Cape  of  Good  Hope. 

(Ventral  aspect.)     One-half  actual  size. 
Fig.    ISC. — Egg-capsule    of    Callorhynchus.      (Peron.)      From  Australia.      (Ventral    aspect.) 

One-half  actual  size. 

rower  proportionately.  Its  emphasized  rugae  arising  from  the  opercular  hinge  are 
more  nearly  transverse,  and,  unlike  any  other  capsule  of  Callorhynchus  known  to  the 
writer,  it  presents  a  thick,  opaque  case,  margined  by  a  thin,  transparent  web.  In 


34 


CHIM^EROID  FISHES  AND  THEIR   DEVELOPMENT. 


the  last  regard  it  differs  again  from  the  capsule  of  fig.  1 5  E,  in  which  the  portion  of 
the  web  in  front  of  the  opercular  hinge  is  far  more  transparent  than  the  posterior 
portion.  Again,  the  capsule  of  fig.  1 5  c,  although  somewhat  resembling  that  of  fig. 
1 5  B,  differs  notably  in  proportions  ;  thus,  the  tail-sheath  is  relatively  longer.  The 
capsule  is  also  much  lighter  in  substance.  A  sixth  and  final  capsule,  fig.  1 5  F 
(Australian),  one  of  several  specimens  in  the  British  Museum,  presents  additional 
differences.  It  is  much  broader  than  the  rest,  and  is  notably  deficient  in  rugulae.* 

I5D 


Fig.  15  D.—  Egg-capsule  of  Callorhynchus.     (Martinez.)     From  Chile.     (Ventral  aspect.)     One-half  actual  size. 

Fig.  15  E. — Egg-capsule  of  Callorhynchus.     (Savatier.)     From  Magellan.     (Ventral  aspect.)     One-half  actual  size. 

Fig.  15  F. — Egg-capsule  of  Callorhynchus.     (British  Museum.)     From  Australia.     ( Dorsal  aspect.)     One-half  actual  size. 

Specimens  similar  to  the  last  mentioned  appear  in  the  museums  of  Copenhagen 
and  of  Harvard  University. 

Other  Callorhynchid  capsules  include  a  fossil  one,  '  'Aletodus"  (Ischyodus),  and 
one  of  the  curious  elongated  forms  from  the  middle  Pacific,  which  has  recently 
been  described  by  Carman.  The  first  (fig.  13),  lately  discussed  by  Jaekel, 
proves  so  similar  to  the  foregoing  recent  capsules  that  one  may  doubt  the  propriety 
of  regarding  it  as  having  belonged  to  a  separate  genus.  The  second,  Carman's  cap- 

*The  specimens,  four  in  number,  in  the  British  Museum,  are  essentially  alike ;  two  were  collected  near  Dunedin, 
two  near  Hobart  (mem,  kindly  furnished  by  Mr.  Boulenger). 


THE   EGG-CAPSULE. 


35 


Fig.  16. —  Chimaeroid  egg-cap- 
sule. Mid-Pacific.  (Ventral 
aspect.)  After  Garman. 
About  two-thirds  natural  size. 

Fig.  17.  —  Egg-capsule  of  Chi- 
maera  monstrosa.  Norway. 


sule  (fig.  1 6),  differs  widely  from  other 
recent  forms.  It  has  thus  a  remark- 
ably long  tail-sheath;  is  provided  with 
a  distinct  type  of  lateral  web,  for  its 
rugae  are  few  in  number  and  restricted 
to  the  region  of  the  trunk-case,  and 
there  are  no  conspicuous  rugae  arising 
from  the  hinge  of  the  opercular  flap, 
dividing  a  precardinal  from  a  post- 
cardinal  lateral  web,  as  in  the  other 
forms. 

These  differences  are  so  striking  that 
I  am  quite  convinced  that  this  capsule 
represents  a  new  genus.*  Garman 
himself  tells  us  nothing  of  its  antece- 
dents, and  as  he  on  one  page  refers 
to  it  as  belonging  to  Callorhynchtts 
antarcticus  and  on  another  to  Callo- 
rhynchus  callorhynchus,  I  infer  that  he 
attributes  it  to  the  latter  species  and 
that  he  regards  these  terms  as  synony- 
mous. 
Chimaera. 

Capsules  somewhat  tadpole-shaped,  with 
large  trunk-sheath,  short  snout-,  and  long, 
tapering  tail-sheath;  lateral  web  narrow,  with 
rugae  faint,  if  present  at  all.  Opercular  flap 
extends  forward  to  end  of  case;  serrulae  pres- 
ent, beginning  far  forward,  a  part  of  the 
complicated  apparatus  of  opercular  ridges 
(cf.  pi.  ni,  fig.  17,  A,  B,  c)  ;  caudal  pores 
many,  opening  on  both  dorsal  and  ventral 
sides.  A  dorsal  keel  present.  Capsules  thin, 
parchment-like,  smooth  or  slightly  ridged. 
The  species  differ  in  well-marked  details,  e-g., 
in  width  of  lateral  web,  length  of  tail-sheath, 
modeling  of  trunk-  and  snout-case,  texture, 
number  of  serrulae,  etc.  If  arranged  in  a  com- 
parative series  (cf.  table,  p.  30,  and  figs- 17,  18, 
21,  22),  C.  colliei stands  closest  to  the  type  of 
Carman's  capsule,  and  C.  mitsukurii  is  ob- 


(Ventral  aspect.)  Natural  size.     viously  the  most  specialized. 


*This  might  be  christened  and  specified  by  a  systematist  who  does  not  hesitate 
ultimatelylto  complicate  Chimaeroid  literature  in  the  matter  of  synonyms.  It  may  be 
long  before  a  new  Chimaeroid  is  fished  from  the  mid- Pacific  and  it  may  be  a  century 
before  this  can  be  satisfactorily  fitted  to  "Carman's  capsule."  Let  us  therefore  pro- 
visionally refer  to  such  capsules  according  to  the  names  associated  with  them — thus 
under  Callorhynchids  we  may  refer  to  the  "  Martinez  capsule, "  "  P^ron  capsule,  "etc. 


CHIM^EROID   FISHES  AND  THEIR   DEVELOPMENT. 


Harriotts  (?). 

Capsule  (fig.  19)  with  case  outlined  like  a  short-handled  spoon;  lateral  web  wide  and  evenly 
transparent,  strengthened  by  an  even  series  of  thickened  costal  ridges.  Dorsal  valve  terminates  in 
a  broad  transverse  lip  subterminal;  its  lateral  rims  have  ruffle-like  serrulae,  which  are  most  marked 
midway  between  hinge  and  anterior  lip,  and  fade  away  anteriorly  and  posteriorly.  No  dorsal  keel; 
on  the  contrary,  a  shallow  groove  extends  along  the  dorsal  wall  of  caudal  sheath.  Caudal  pores  in 
a  series  of  decided  slits;  the  largest,  in  the  middle  of  the  series,  open  ventrad,  although  they  appear 
also  on  the  dorsal  side  as  a  marked  surf  ace  feature  of  the  capsule.  Capsule  smooth,  parchment-like,  pale. 
iS  i  20 


Fig.  18. — Egg-capsule  of  Chimaera  colliei.     Puget  Sound.     (Ventral  aspect.)     Natural  size. 

pig.  |9.— Egg-capsule  of  Harriotta  (?) .        North  Atlantic.        After  specimen  preserved  in  U.  S.  National 

Museum.     (Ventral  aspect.)     Natural  size. 
Fig.  20. —  Egg-capsule  of  Rhinochimaera  indica  ("  Callorhynchus  indicus  ").      Indian  Ocean.      After  Alcock. 

(Ventral  aspect.)     Three-quarters  natural  size. 

This  interesting  specimen  is  preserved  in  the  National  Museum  at  Washington, 
where  it  bears  the  number  22793.  The  present  writer  is  indebted  to  the  Curator 
of  the  Department  of  Fishes,  Mr.  Barton  A.  Bean,  for  his  courtesy  in  bringing  it 
to  his  attention,  and  to  the  Museum  for  the  privilege  of  describing  it.  Its 
history  is  briefly  as  follows:  It  was  taken,  1879  (on  trawl  line),  by  the  Gloucester 
fishing  vessel  of  Capt.  G.  A.  Johnson,  in  water  of  375  fathoms,  lat.  42°  47',  long. 
63°  10'.  It  obviously  does  not  belong  to  the  foregoing  genera,  but  from  its  resem- 


THE   EGG-CAPSULE. 


37 


21 


22 


Fig.  21. — Egg-capsule   of  Chimaera  phan- 

tasma.     Misaki,  Japan.    (Ventral  aspect.} 

Natural  size. 
Fig.  22. — Egg-capsule    of    Chimaera    mit- 

sukurii.  Misaki,  Japan.    (Ventral  aspect.) 

Natural  size. 


blance  to  Rhinochimsera  it  evidently 
belonged  to  a  similar  fish.  It  is  thus  to 
be  attributed,  with  strong  probability,  to 
the  only  Chimseroid  of  this  character 
known  from  the  region  in  which  it  was 
taken,  i.  e.,  Harriotta.* 

A  second  capsule  (fig.  20),  hitherto 
associated  with  Callorhynchus,  should 
provisionally  be  placed  with  the  present 
genus.  Although  collected  in  the  Indian 
ocean,  it  .resembles  closely  the  capsule 
from  the  Atlantic,  having  the  same  type 
of  lateral  web,  costae,  and  subterminal 
opercular  margin,  f 

Rhinochimaera. 

Capsule  with  case  spindle-shaped;  snout-sheath 
stouter  and  thicker  than  tail-sheath;  lateral  web 
wide,  its  outer  margin  transparent,  strengthened 
by  a  regular  series  of  tapering  costse.  Lip  of 
dorsal  valve  ends  in  a  narrow,  delicate  lip,  sub- 
terminal.  Serrulse  low  and  faint.  No  dorsal  keel; 
in  its  place  a  shallow  groove  extends  along  the 
dorsal  wall  of  the  caudal  sheath.  Caudal  pores 
similar  to  those  in  Harriotta  (?).  Capsules 
smooth,  dark-colored,  hornlike. 

The  capsule  shown  in  fig.  23  has  been 
definitely  associated  with  the  species 
R.  pacifica.  It  differs  notably  from 
the  Indian  capsule  in  proportions,  in  the 
number  and  character  of  its  costae,  and 
in  its  operculum. 

On  the  foregoing  pages  the  egg-cap- 
sules of  Chimgeroids  have  been  referred 
to  in  considerable  detail,  since  by  a  com- 
parison of  their  characters  light  is  thrown 
upon  the  problem  of  Chimseroid  descent. 
For  it  is  clear  that  the  different  species 
of  Chimasroids  produce  capsules  specific- 
ally distinct;  and  it  follows,  therefore, 
in  the  light  of  evolutional  analogies,  that 
the  fishes  which  produced  the  more 
differentiated  capsules  are  the  descend- 
ants of  those  in  which  simpler  capsular 
structures  prevailed.  It  follows,  also, 
conversely,  that  the  forms  which  have 
the  simpler  capsules  are  apt,  in  this  and 
other  regards,  to  represent  more  closely 
the  common  ancestor.  This  evidence, 


* Harriotta  has  been  taken  between  lat.  36°  and  40°,  long.  70°  and  75°;  from  greater  depth,  however — 700  to  1,100 

fathoms.      The  latter  difference  is  not  all-important,  as  by  many  analogies  spawning  might  well  occur  at  a  lesser  depth. 

fThe  writer  recently  examined  this  specimen  in  the  Calcutta  museum,  through  the  courtesy  of  Major  Alcock. 


CHIMyEROID   FISHES  AND  THEIR   DEVELOPMENT. 


Fig.    23. — Egg-capsule    of    Rliinorliimaera     pacifica.     Misaki. 
(Ventral  aspect.)     Natural  size. 


however,   may  best  be  considered  subse- 
quently in  correlation  with  similar  facts. 

The  capsules  may  also  be  referred  to 
at  the  present  time  in  the  evidence  they 
present  regarding  the  factors  of  evolution  ; 
for  it  is  clear  that  such  highly  specialized 
capsules  provide  a  valuable  check  upon 
the  evolutional  process  from  the  standpoint 
of  the  obvious  "prevision"  which  they 
demonstrate.  The  capsule  is,  in  short, 
adapted  not  so  much  to  the  egg  as  to 
the  young  fish  which  it  will  later  contain. 
Thus  it  is  specialized  in  accord  with  the 
shape  of  the  young  fish,  its  position,  and 
its  late  physiological  needs,  all  to  a  de- 
gree which  is,  indeed,  probably  unequaled 
in  the  secondary  embryonic  membranes  of 
other  animals.  *  This  degree  of  special- 
ization becomes  clearer,  moreover,  when 
we  take  into  consideration  the  formation 
of  the  capsule. 

FORMATION  OF  THE  CAPSULE. 

At  the  time  the  egg  is  about  to  leave 
the  ovary  the  oviduct  is  flaccid  and  is 
richly  suffused  with  blood  ;  in  fact,  from 
this  time  onward  the  oviducal  sinus f  in 
which  they  lie  is  dilated  (plate  i,  fig.  4, 
and  plate  n,  fig.  5,  ovd.  s.\  forming  a 

* ' Cf.  Dean,  1904,  Biol.  Bulletin,  vol.  vn,  pp.  105-112. 

t  These  sinuses  arise  in  the  mesovaria,  the  walls  of  which 
do  not  become  apposed.  They  are  thus  longitudinal  sacs  of 
blood  in  which  the  oviducts  lie  more  or  less  freely,  depend- 
ing upon  the  degree  of  development  of  the  egg-capsule 
(cf.  plate  11,  fig.  5,  and  plate  i,  fig.  4,  left  oviduct).  In  the 
former  figure,  however,  this  condition  is  not  seen  favorably, 
since  the  oviduct  is  purposely  pushed  against  the  wall 
of  its  sinus,  thus  dislodging  the  opaque  blood,  so  that  the 
structures  of  the  oviduct  can  be  better  described.  In 
the  latest  stage  in  the  formation  of  the  capsule,  on  the  other 
hand,  the  sinus  is  so  filled  with  the  enlarged  oviduct  that  in 
ventral  view  it  can  hardly  be  seen  ;  thus  in  the  figure  the 
oviducts  appear  to  lie  freely  in  the  body-cavity.  The  blood 
supply  in  the  sinus,  it  may  be  remarked,  is  maintained  by 
direct  communication  with  the  cardinal  (not  to  complicate 
the  problem  as  to  the  relations  with  the  renal  portal )  blood- 
cavities.  Between  the  lines  where  the  mesovarial  folds  are 
attached  to  the  dorsal  body  wall  a  row  of  ostia  is  present 
( pi.  i,  fig.  4,  o).  This  method  of  increasing  enormously  the 
oviducts'  blood  (venous)  supply  is  evidently  correlated  with 
the  rapid  formation  of  the  highly  complicated  egg-capsule. 
It  can  hardly  be  regarded  as  evidence  of  a  primitive  gon- 
adial  sinus,  and  we  are  led  to  conclude  that  morphologically 
the  veins  of  the  mesovarium  have  coalesced,  leaving  ostia 
as  vestiges  of  the  gonadial  veins,  e.  g.,  of  sharks. 


THE  EGG-CAPSULE.  39 

remarkable  venous  outlet,  and  the  arterial  supply  is  also  highly  developed,  branches 
of  the  oviducal  artery  passing  backward  along  the  oviduct  and  dividing  into  an 
elaborate  series  of  transverse  branchlets.  * 

The  oviduct  itself  undergoes  striking  changes  to  accomplish  step  by  step  the 
stages  in  the  formation  of  the  capsule.  To  follow  these  briefly,  the  oviduct  con- 
tracts cephalad  when  the  egg  is  received,  and  holds  it  in  the  cavity  dilated  in  the 
posterior  region  of  the  capsular  gland.  Here  it  is  that  the  walls  of  the  oviduct 
form  folds  and  ridges  and  by  these  are  able  to  model  the  secretion  of  the  gland 
into  the  beginnings  of  the  capsule.  From  such  a  position  the  early  capsule  was 
obtained  which  is  figured  in  plate  in,  figure  12.  Jts  shell  was  papery,  whitish  (with 
but  a  trace  of  color),  and  so  frail  that  it  could  not  be  removed  unbroken  with  the 
contained  egg. 

The  exact  mode  of  folding  of  the  walls  of  the  oviduct  to  produce  the  details  of 
the  capsule  need  not  be  given  in  detail.  The  growth  in  the  capsule  continues,  as 
shown  in  plate  in,  figs.  13,  14,  15,  and  16,  the  tail-sheath  and  its  appendage  of 
the  case  being  the  last  portions  formed.  The  fact  that  the  anterior  part  of  the 
case  is  finished  before  the  tail-sheath  was  often  taken  advantage  of  by  the  writer  in 
his  effort  to  secure  embryological  material,  for  he  found  that  such  an  egg  as  shown 
in  plate  n,  fig.  8,  could  be  safely  incubated  for  earlier  stages  if  the  base  of  the  tail- 
sheath  was  kept  closed,  e.  g.,  by  a  ligature. 

In  comparing  the  foregoing  figures  one  observes  a  number  of  details  as  to  the 
modeling  of  the  capsule  from  stage  to  stage.  The  earliest  condition  (plate  in,  fig.  1 2), 
shows  that  the  tip  of  the  capsule,  although  delicate,  is  almost  complete,  with 
opercular  folds,  serrulae,  apex,  lateral  ridges,  and  the  beginnings  of  the  dorsal 
keel.  In  the  stage  of  plate  in,  fig.  16,  the  capsule  is  practically  complete,  save  for 
the  tail-sheath,  and  in  this  stage  the  lateral  webs  are  widest,  suggesting  the  con- 
ditions of  Callorhynchus. 

The  oviduct  from  which  such  a  stage  is  taken  as  that  shown  opened  in  plate  n, 
fig.  6,  forms,  as  we  could  naturally  expect,  an  exact  mold  for  the  capsule.  Thus  we 
find  a  cervix,  c,  with  sphincter  (for  apex  of  the  case) ;  distinct  creases,  /.  w.  (for  lateral 
webs)  ;  a  thickened  tract,  with  folded  margins  and  with  median  groove,  d.  k.  (for 
dorsal  wall  of  case,  opercular  folds,  and  dorsal  keel).  As  the  tail-sheath  was  not 
yet  developed  in  this  capsule,  the  corresponding  region  of  the  oviduct,  /.  s.,  is  still 
contracted ;  but  at  the  sides  we  note  the  broader  folds,  r,  in  which  the  ruga=:  are 
laid  down  ;  also  at  t.  o.  the  deep  recesses  below  the  capsular  gland  in  which  the 
terminal  organ  comes  to  be  formed.  At  a  subsequent  stage  the  lateral  webs  are 
strengthened  by  a  process  of  folding,  which  causes  them  to  become  narrower  (cf. 
plate  11,  fig.  10,  and  plate  in,  fig.  16)  ;  and  at  the  same  time  the  tail-sheath  is  laid 
down  (plate  i,  fig.  i). 

In  the  latter  process  the  sheath  itself,  with  the  beginnings  of  its  caudal  pores, 
is  formed  before  the  adjacent  web  (plate  11,  fig.  7),  and  when  this  is  completed  there 
remains  to  be  formed  only  the  capsular  filament  and  adhesive  organ.  By  this  time, 
however,  the  capsule  has  acquired  such  a  phenomenal  length  that  it  extends  from 
the  oviducal  (i.  e.  retroanal)  opening  forward  to  the  anterior  wall  of  the  body-cavity 

*  The  oviducal  artery  divides  into  four  branches  when  it  reaches  the  anterior  end  of  the  capsular  gland,  two  beccm- 
ing  dorsal,  two  ventral,  and  thus  they  proceed,  bilaterally  arranged,  as  far  as  the  posterior  portion  of  the  oviduct  (cf. 
plate  i,  fig.  i ;  plate  n,  figs.  5  and  7 ). 


40  CHIM^EROID   FISHES  AND  THEIR   DEVELOPMENT. 

terminating  near  the  cardiac  region.  To  add,  therefore,  a  couple  of  inches  to  the 
length  of  the  capsule  involves  a  serious  problem  in  the  matter  of  space.  This  has 
been  solved  as  follows  :  The  capsule  is  gradually  released,  so  that  it  comes  to  project 
from  the  fish's  body  ;  at  first  the  apex  appears  at  the  mouth  of  the  oviduct,  then 
the  trunk-sheath,  then  the  tail-sheath  (fig.  1 2).  If  at  this  time  the  egg  is  dislodged, 
an  abortive  terminal  results,  as  in  plate  n,  fig.  10.  If  it  remains,  the  process  in  the 
formation  of  the  capsular  filament  and  terminal  organ  progresses  as  seen  in  plate  i, 
fig.  4.  The  capsule  now  protrudes  as  far  as  the  base  of  the  filament,  and  with  this 


26 


Figs.  24-26. — Egg-capsules  of  Chimaera  colliei,  partly  opened,  so  as  to  show  egg  and  young.     Natural  size. 
24.  Late  blastula  (about  9  days).     25.  Early  gattrula  (about  19  days).     26.  Late  gastrula  (about  24  days). 

protrusion  occur  many  changes  in  the  oviduct  (cf.  plate  u,  fig  4,  and  plate  n,  fig.  6), 
e.  g. ,  its  diameter  becomes  greatly  constricted  and  its  dorsoventral  characters  and 
web  creases  obsolescent  ;  it  also  loses  its  earlier  differentiation  into  trunk-sheath 
and  tail-sheath  forming  portions,  and  its  vaginal  region  is  extended  headward,  the 
remaining  part  of  the  oviduct  becoming  correspondingly  reduced.  All  these  changes 
are  to  the  obvious  end  of  molding  the  long  capsular  filament  and  the  bulbous  terminal 
organ  (plate  i,  fig.  4,  c.  f. ,  and  c.  o. ).  For  the  formation  of  the  latter  serves  a  special 
region  of  the  capsular  gland,  i.  e.,  its  hindmost  zone,  a  portion  pinkish  in  color, 
provided  with  the  recesses  into  which  the  terminal  organ  has  been  traced.  * 

*  Finally,  a  note  may  be  given  as  to  the  probable  mode  of  attachment  of  the  capsule  (cf,  pp.  26,  27.)  It  is  evident 
that  the  oviduct  can  be  greatly  evaginated  at  the  time  the  egg  is  deposited  (plate  i,  fig.  2\  and  with  this  phenomenon 
is  evidently  connected  the  forward  extension  of  the  cervix  (cf.  plate  i,  fig.  4,  and  plate  n,  fig.  6).  We  may  thus 
conclude  that  at  the  cervix,  then,  the  bulbous  organ  of  attachment  can  be  held  by  the  fish  even  when  the  oviducts  have 
been  greatly  everted  ;  and  it  would  naturally  be  by  such  elongated,  even  finger-like,  processes  that  the  fish  could  press 
the  filamentous  ends  of  the  capsules  against  the  object  of  attachment,  e.  g-.,  a.  rock  fragment,  and  thus  secure  their 
adhesion. 


THE   EGG-CAPSULE.  4-1 

Before  describing  the  various  stages  of  Chimsera  (C.  colliei)  a  brief  survey  of 
the  general  plan  of  development  might  be  given  (cf.  Biol.  Bulletin,  1903,  vol.  iv, 
No.  5,  pp.  270-286): 

The  development  is  shark-like  (figs.  24-29).  In  early  stages  a  small  germinal 
area  is  present.  In  this  polyspermy  occurs,  then  a  cleavage,  in  which,  however, 
surface  furrows  are  retarded.  The  early  gastrula  suggests  somewhat  closely  the 
condition  in  shark,  or  rather  in  ray,  but  the  blastopore  appears  near  instead  of  at 
the  margin  of  the  blastoderm.  The  embryo  develops  a  long,  delicate  tail,  external 
gills,  and  a  head  terminating  in  a  conspicuous  frontal  -"lobe."  It  absorbs  the  yolk- 


29 


28 


Figs.  27-29. — Egg-capsules  of  Chimaera  colliei,  partly  opened,  so  as  to  show  egg  and  young.     Natural  size. 

27.  Early  embryo  (about  32  days),  showing  subdivision  of  yolk  material. 

28.  Late  embryo  (about  5  months),  showing  external  gills  and  miniature  sac.     At  this  rime  the  embryo  is  bathed  in  a  heavy  milky  fluid  resulting 

from  continued  subdivision  of  yolk  masses. 

29.  Young  Chimaera  at  about  the  time  of  hatching    ?  eight  months).        The  capsule  at  this  period  is  greatly  weathered  and  develops  a  tension 

which  probably  aids  the  operculum  in  springing  open  and  permitting  the  young  to  escape. 

sac,  and  before  hatching  becomes  large  in  size  and  has  many  features  of  the  adult, 
e.  g. ,  mixipterygia  in  the  case  of  the  male.  By  far  the  most  remarkable  feature 
during  this  process  of  development  is  the  behavior  of  the  yolk.  This  undergoes 
vacuolization,  followed  by  fragmentation.  Of  the  yolk  a  small  portion  only  is 
inclosed  within  the  sac  of  the  young  ;  the  remainder  continues  to  fragment,  form- 
ing a  creamy  mass  which  nourishes  the  embryo  via  external  gills  and  gut.  The 
fragmentation,  we  have  reason  to  believe,  is  an  extreme  modification  of  the  process 
of  cleavage. 


42  CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 

THE  EGG  AND  ITS  MEMBRANES. 

In  the  newly  deposited  capsule  the  egg  measures  35  by  20  by  12  mm.,  but  it  is 
smaller,  together  with  the  capsule,  if  taken  from  young  fish  (cf.  the  size  of  the 
capsules  shown  in  plate  n,  fig.  10,  and  plate  in,  fig.  17),  as  is  also  the  case  in  sela- 
chians (Riickert).  Its  consistency  becomes  less  fluid-like  as  development  advances; 
thus,  shortly  before  breaking  from  the  ovarian  membrane,  the  egg  has  so  little  con- 
sistency that  it  will  flatten  out  to  the  diameter  of  about  45  mm.  (plate  n,  fig.  5). 
Its  ellipsoidal  outline  is  assumed  when  inclosed  in  the  capsule.  It  will,  however, 


32 


Fig.  30. — Early  ovarian  egg  of  Chimaera  colliei.  Section  through  major  axis  of  egg.  ffs,  Gonadial  sinus;  £-<',  germinative  vesicle  — 
around  it  the  extent  of  the  space  indicates  the  size  of  vesicle  before  fixation ;  o,  stalk  attaching  egg  to  ovary  and  inclosing  the 
arterial  blood  supply;  /,  peritoneum;  /,  tunic (=  granulosa). 

Figs.  31  and  32. — Sections  of  the  marginal  region  of  ovarian  eggs  (the  first  measuring  about  5  mm.  in  diameter,  the  second  about  15  mm.), 
indicating  changes  in  the  tunic  and  the  development  of  yolk,  bm.  Basement  membrane  ( between  the  tunic  and  the  egg  ) ; 
by,  botryoidal  yolk  masses  developed  in  vacuoles  in  germinal  yolk ;  c,  layers  of  connective  and  vascular  tissue  theca  in  ovarian 
membrane  surrounding  egg;  ffx,  gonadial  sinus;  p,  peritoneum;  /.tunic  of  ovarian  tissue  inclosing  egg  (follicular  epithelium); 
/,  inmost  layer ;  »;,  middle  layer ;  o,  outmost  layer ;  zr,  zona  radiata.  X  585. 

present  an  almost  spherical  form  (horizontal  outline  25  by  20  mm.)  if  the  constricting 
capsule  be  opened  (plate  n,  fig.  8).  In  later  stages  it  has  the  consistency  of  thick 
cream. 

THE  OVARIAN  MEMBRANES. 

Comparison  with  corresponding  stages  in  shark  (Pristiurus)  shows  that  the 
wrappings  of  the  ovarian  eggs  of  Chimaera  are  the  more  complex.  In  early  stages  of 
the  latter  the  ovarian  tunic  is  thicker  and  its  nuclear  elements  more  abundant  and 
more  evidently  specialized.  Thus  in  fig.  30,  which  shows  in  section  an  egg  of  about 
5  mm. ,  one  notes  the  thickness  of  the  tunic ;  this  (greatly  enlarged)  is  shown  in 


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43 

:ial  in  character,  is  clearly 
middle,  and  inmost.  In 
essed — oblong,  therefore, 
ley  are  large  and  diffuse  ; 
he  basement  membrane, 
lial  sinus,  gs,  the  tissue  of 
interspersed  with  plasma 
issed  through  the  special- 
ay  be  assumed  that  the 
us  the  closely  compacted 
plasma  spaces  (and  capil- 
hese  again  transfer  their 
1  the  egg. 


33C 


)  mm.  in  diameter),    gy.  Germinal 
oup  of  chromosomes  ;  mgT,  limiting 


region  of  the  zona  radiata.     In  this 

.  vesicle  recedes  from  surface  of  egg. 
c,  showing  large  vacuoles  ;  :,  zona 
•n  the  vesicle  and  the  adjacent  tunic 


rently  physiological,  since 
:leus  of  the  inmost  layer 
is  clearly  connected  with  a  nucleus  ot  the  middle  layer.  ~In  some  cases  such  a  rela- 
tionship is  demonstrated  by  dividing  nuclei,  which,  it  may  be  remarked,  exhibit 
sometimes  direct,  sometimes  indirect  division.  At  the  surface  of  the  egg  is  a  sharply 
marked  membrana  limitans ;  below  this,  irregular  in  thickness,  a  zona  radiata,  prob- 
ably homologous  with  the  well-known  layer  in  eggs  of  other  fishes.  Below  this  the 
egg  shows  an  outer  finer  layer  and  an  inner  coarser  or  reticular  layer,  in  which 
large  vacuoles  frequently  occur.  At  a  somewhat  later  stage  (egg  measuring  about 


CHIM/ER( 


In  the  newly  deposite 
smaller,  together  with  th< 
capsules  shown  in  plate  n, 
chians  (Riickert).  Its  con 
thus,  shortly  before  breakii 
sistency  that  it  will  flatte 
Its  ellipsoidal  outline  is  a 


Fig.  30. — Early  ovarian  egg  of  Chimaera  co 
around  it  the  extent  of  the  space  intlii 
arterial  blood  supply;  />,  peritoneum; 

Figs.  3 1  and  32. — Sections  of  the  marginal 
indicating  changes  in  the  tunic  and  I 
by,  botryoidal  yolk  masses  developei 
membrane  surrounding  egg;  gs,  gona 
i,  inmost  layer;  m,  middle  layer;  o, 

present  an  almost  spherica 
capsule  be  opened  (plate  i 
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THE  OVARIAN  MEMBRANES. 


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42  maps. 


43 

rtial  in  character,  is  clearly 
,  middle,  and  inmost.  In 
ressed — oblong,  therefore, 

hey  are  large  and  diffuse  ; 
the  basement  membrane, 
dial  sinus,  gs,  the  tissue  of 

interspersed  with  plasma 
•assed  through  the  special- 
aay  be  assumed  that  the 
lus  the  closely  compacted 

plasma  spaces  (and  capil- 
These  again  transfer  their 
o  the  egg. 


33  D    y 


W'      . 


10  mm.  in  diameter).     <•  v,  Germinal 
;roup  of  chromosomes ;  mgT,  limiting 

s  region  of  the  zona  radial  a.     In  this 

11  vesicle  recedes  from  surface  of  egg. 
tic,  showing  large  vacuolcs ;    : ,   zona 
:en  the  vesicle  and  the  adjacent  tunic 


irently  physiological,  since 
icleus  of  the  inmost  layer 

is  clearly  connected  with  a  nucleus  ot  tne  middle  layer. In  some  cases  such  a  rela- 
tionship is  demonstrated  by  dividing  nuclei,  which,  it  may  be  remarked,  exhibit 
sometimes  direct,  sometimes  indirect  division.  At  the  surface  of  the  egg  is  a  sharply 
marked  membrana  limitans ;  below  this,  irregular  in  thickness,  a  zona  radiata,  prob- 
ably homologous  with  the  well-known  layer  in  eggs  of  other  fishes.  Below  this  the 
egg  shows  an  outer  finer  layer  and  an  inner  coarser  or  reticular  layer,  in  which 
large  vacuoles  frequently  occur.  At  a  somewhat  later  stage  (egg  measuring  about 


CHIM^RC 


In  the  newly  depositec 
smaller,  together  with  the 
capsules  shown  in  plate  u, 
chians  (Riickert).  Its  cons 
thus,  shortly  before  breakir 
sistency  that  it  will  flattei 
Its  ellipsoidal  outline  is  a; 


Fig.  30. — F.arly  ovarian  egg  of  Chimaera  col 
around  it  the  extent  of  the  space  indie 
arterial  blood  supply ;  /,  peritoneum ;  i 

Figs.  3 1  and  32. — Sections  of  the  marginal 
indicating  changes  in  the  tunic  and  t 
by,  botryoidal  yolk  masses  developec 
membrane  surrounding  egg;  g-x,  gona 
/.  inmost  layer ;  /;; ,  middle  layer ;  o, 

present  an  almost  spherica 
capsule  be  opened  (plate  i  . 
cream. 


No. 


No. 


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November  17,  1906. 


THE  OVARIAN  MEMBRANES. 


Comparison  with  corresponding  stages  in  shark  (Pristiurus)  shows  that  the 
wrappings  of  the  ovarian  eggs  of  Chimxra  are  the  more  complex.  In  early  stages  of 
the  latter  the  ovarian  tunic  is  thicker  and  its  nuclear  elements  more  abundant  and 
more  evidently  specialized.  Thus  in  fig.  30,  which  shows  in  section  an  egg  of  about 
5  mm. ,  one  notes  the  thickness  of  the  tunic  ;  this  (greatly  enlarged)  is  shown  in 


THE  EGG  AND  ITS  MEMBRANES. 


43 


fig  3 1 ;  here  it  will  be  seen  that  the  tunic,  although  syncytial  in  character,  is  clearly 
divided  according  to  its  nuclei  into  three  layers — outmost,  middle,  and  inmost.  In 
the  outmost  layer  the  nuclei  are  small  and  closely  compressed — oblong,  therefore, 
in  form — and  directed  ecto-entad ;  in  the  middle  layer  they  are  large  and  diffuse  ; 
in  the  inmost,  small,  irregular,  and  closely  apposed  to  the  basement  membrane. 
Between  the  outmost  layer  of  the  tunic,  o,  and  the  gonadial  sinus,  gs,  the  tissue  of 
the  ovary  contains  numerous  strands  of  connective  tissue  interspersed  with  plasma 
spaces,  c;  it  is  from  these,  doubtless,  that  nutriment  is  passed  through  the  special- 
ized tunic  to  the  inclosed  egg.  During  this  process  it  may  be  assumed  that  the 
various  types  of  nuclei  of  the  tunic  play  definite  parts  ;  thus  the  closely  compacted 
nuclei  of  the  outmost  layer  purvey  nutriment  from  the  plasma  spaces  (and  capil- 
laries) to  the  dilated  elements  of  the  middle  layer.  These  again  transfer  their 
nutriment  to  the  small  nuclei  which  are  closely  apposed  to  the  egg. 


.33* 


Fig.  33. — Section  of  region  of  germinative  vesicle  of  well-grown  ovarian  egg  (about  20  mm.  in  diameter),  gy.  Germinal 
yolk;  gs,  gonadial  sinus;  gv,  large  germinal  vesicle  containing  near  its  center  a  group  of  chromosomes;  mgv,  limiting 
membrane  of  germinal  vesicle  ;  t,  tunic ;  zr,  zona  radiata. 

Fig.  33A. — Detail  of  preceding  section  from  point  at  side  of  egg,  showing  absence  in  this  region  of  the  zona  radiata.  In  this 
region  yolk  granules  are  developed  in  numerous  minute  vacuoles. 

Fig.  33B. — Detail  of  section  of  fig.  33,  taken  at  a  point  where  the  side  of  the  germinal  vesicle  recedes  from  surface  of  egg. 
gy,  Germinative  yolk ;  mgi',  membrane  forming  wall  of  germinal  vesicle ;  /,  tunic,  showing  large  vacuoles ;  z,  zona 
radiata.  This  will  be  seen  to  extend  only  over  the  margin  of  the  vesicle.  Between  the  vesicle  and  the  adjacent  tunic 
there  extends  only  a  thin  peripheral  layer  of  germinative  yolk. 

Figs.  33C  and  33D. — Detail  of  chromosomes  shown  in  fig.  33  (two  sections).      X  385. 

The  differences  in  the  nuclei  of  the  tunics  are  apparently  physiological,  since 
intergrading  forms  occur  ;  thus  in  the  figure  cited  a  nucleus  of  the  inmost  layer 
is  clearly  connected  with  a  nucleus  of  the  middle  layer.  In  some  cases  such  a  rela- 
tionship is  demonstrated  by  dividing  nuclei,  which,  it  may  be  remarked,  exhibit 
sometimes  direct,  sometimes  indirect  division.  At  the  surface  of  the  egg  is  a  sharply 
marked  membrana  limitans ;  below  this,  irregular  in  thickness,  a  zona  radiata,  prob- 
ably homologous  with  the  well-known  layer  in  eggs  of  other  fishes.  Below  this  the 
egg  shows  an  outer  finer  layer  and  an  inner  coarser  or  reticular  layer,  in  which 
large  vacuoles  frequently  occur.  At  a  somewhat  later  stage  (egg  measuring  about 


44 


CHIM^JROID   FISHES  AND  THEIR   DEVELOPMENT. 


15  mm.)  the  conditions  of  the  tunic  have  changed.  It  has  become  thinner  (fig.  32) 
and  has  modified  its  structures  considerably.  In  place  of  the  differentiated  inmost, 
middle,  and  outmost  layers,  an  outer  layer  is  alone  conspicuous  and  even  here  the 
nuclei  have  not  the  crowded  character  of  the  earlier  stage  ;  the  inmost  and  middle 
layers  have  merged,  forming  a  somewhat  indefinite  layer,  poor  in  nuclei.  In  some 
cases  markings  in  the  (partial)  syncytium  indicate  that  the  tunic  is  in  places  but  one 
cell  thick.  Indirect  divisions  sometimes  occur.  The  entire  structure  of  the  tunic 
suggests  that  closer  physiological  relations  exist  between  the  vascular  supply,  on 
the  one  hand — plasma  spaces,  as  in  c,  having  now  extensively  drawn  together  into 


d 


•cy 


•Sf 


Fig.  34. — Section  of  germinal  region  of  egg  of  Chimeera  colliei  during  stage  of  early  fertilization.  cy.  Coarse 
yolk ;  li,  dendritic  lines  marking  paths  of  sperms ;  fy,  fine  yolk ;  gp,  germinal  area  extending  as  a 
plug-shaped  mass  deep  into  the  egg ;  n,  nuclei,  sperm,  and  egg  fusing.  Under  the  points  marked  with 
asterisks  (*)  vacuoles  occur  which  separate  masses  of  fine  germinal  yolk  and  are  usually  found  to  contain 
sperm  nuclei. 

capillaries — and  the  egg  on  the  other.  This  physiological  process  is  doubtless  aided 
by  the  thinning  of  the  membrana  limitans,  bm,  and  of  the  zona  radiata.  And  as 
an  indication  that  the  nutriment  is  being  passed  rapidly  into  the  yolk  we  observe 
that  even  close  to  the  surface  of  the  egg  large  yolk  masses  are  appearing. 

In  a  final  stage  of  the  ovarian  egg  the  tunic  is  still  further  diminished  in  thickness 
(figs.  33,  33  A).  It  is  reduced,  in  fact,  to  a  single-celled  layer,  of  which  the  nuclei 
are  usually  disposed  nearer  the  outer  wall  in  the  same  niveau.  Sometimes,  however, 
they  are  closely  apposed  to  the  inner  wall,  but  in  all  cases  they  are  of  the  same 
general  character  (fig.  33  B),  i.  e.,  spherical  nuclei,  with  sharply  marked  mem- 
brane, showing  but  faint  traces  of  chromatin  meshwork,  but  with  one  or  two  con- 


THE  EGG  AND  ITS  MEMBRANES.  45 

spicuous  nucleoles.  Cell  boundaries  are  sometimes  better  seen  than  in  earlier 
stages,  and  large  vacuoles  are  present  near  the  tunic's  outer  wall ;  surrounding  this 
the  ovarian  stroma  is  reduced  to  practically  a  single-celled  layer,  which  now  alone 
separates  the  tunic  from  the  blood  in  the  large  gonadial  sinus  ( fig.  33,  gs).  Com- 
parison with  earlier  stages  thus  indicates — paradoxical  as  the  statement  reads — that 
the  arterial  supply  of  the  developing  egg  is  progressively  diminished  and  the  venous 
supply  progressively  increased.* 

The  foregoing  details  are  given,  since  they  indicate  the  complexness  of  the 
problem  of  the  growth  of  the  egg  in  Chimaera.  There  here  exist  at  various  stages 
not  a  tunic  of  an  almost  unvarying  character,  as  apparently  is  the  case  in  sharks, 
but  one  which  in  earlier  stages  is  shark-like,  but  which  later  changes  progressively, 
diminishing  its  thickness  and  reducing  the  number  of  its  component  elements,  to 
the  end  that  each  cell  of  this  membrane  comes  in  immediate  contact  on  the  one 
hand  with  the  egg  and  on  the  other  with  the  nutritive  fluid.  It  is  further  clear  that 
the  elements  of  the  tunic  acquire  changed  physiological  characters  as  development 
proceeds — witness  the  changes  which  occur  in  size,  shape,  and  disposition  of  the 
nuclei,  the  appearance  of  vacuoles  in  the  late  stage — pari  passu  with  changes  in  the 
arrangement  of  the  blood  supply. 

YOLK. 

The  yolk  masses  at  first  occur  in  the  granular  ooplasm  close  to  the  zona;  next 
they  appear  in  vacuoles,  cavities  which  are  noted  before  the  appearance  of  the  yolk 
masses,  and  are  later  seen  to  become  greatly  enlarged  and  to  be  drawn  together 
around  the  masses  of  yolk.  The  yolk  itself  increases  in  bulk,  its  masses  now  often 
presenting  irregular  protuberances,  resulting  apparently  from  a  process  of  accretion. 
In  surface  view  many  of  the  yolk  masses  appear  botryoidal  (in  eggs  preserved  in 
sublimate,  acetic-sublimate,  picro-sulphuric,  picro-formalin).  And  this  condition 
persists  while  the  egg  is  attaining  its  mature  size.  In  stages  as  late  as  gastrulation 
the  coarse  yolk  differs  little  outwardly  from  the  foregoing  conditions.  The  grains 
show  only  a  smoother  surface  and  a  possible  tendency  to  coalesce  ;  but  it  is 
evident  that  the  vacuoles  are  now  more  closely  adjusted  to  the  yolk.  The  fine 
yolk,  on  the  other  hand,  is,  as  Riickert's  figures  indicate  in  sharks,  derived  from 
the  coarse  yolk  by  a  process  of  subdivision.  Comparing  the  earlier  stage  (fig.  32) 
with  one  at  fertilization  (fig.  35),  we  observe  that  the  substance  of  the  former  grains 
has  become  subdivided  into  morula-like  masses  of  minute  deutoplasmic  elements, 
these,  as  before,  lying  in  large  vacuoles.  In  each  of  these  masses  one  notes  that 
there  has  usually  been  produced  a  globule  of  a  highly  refringent  substance  analo- 
gous to  the  oil-drop  of  the  teleostean  egg.  In  a  later  stage  the  corresponding  por- 
tion of  the  egg  has  become  a  well-defined  region  of  germinal  yolk  (Riickert's  Keim- 
dotter),  and  we  are  led  to  conclude  that  the  later  condition,  with  fine  grains  of  yolk, 
is  the  result  of  a  continued  process  of  subdivision  of  the  morula-like  masses  and 
their  subsequent  confluence.  (The  general  character  of  the  germinal  yolk  is  shown 
in  figs.  33  A  and  33  B  aigy.) 

*  In  its  latest  stage  the  ovarian  egg  shows  a  series  of  capillaries  (plate  n,  fig.  5),  converging  to  an  elliptical  stigma. 
Unfortunately,  the  relations  of  the  tunic  in  this  stage  were  not  examined. 


46  CHIM^EROID   FISHES  AND  THEIR   DEVELOPMENT. 

The  grouping  of  the  yolk  elements  in  the  mature  egg  is  somewhat  irregular. 
Sometimes  "drifts"  of  germinal  yolk  underlie  the  coarse  yolk;  sometimes  they 
extend  obliquely,  admitting  between  them  inbursts  of  coarser  yolk.  In  general,  at 
the  time  of  fertilization,  the  germinal  yolk  dips  deeply  down  into  the  coarse  yolk, 

36 


35 


Fig,  35. — Section  of  fertilization  stage,  showing  near  the  surface  and  at  the  side  of  the  germinal  area  a  sperm  which  has  just  gained 
entrance.  This  is  shown  at  .•>•,  surrounded  by  a  lighter  area  of  germinal  material.  In  the  depression  above  the  sperm  is  a  mucus, 
like  mass  which  may  represent  in  part  the  tail  of  the  sperm.  «/,  Middle  piece.  X  575. 

Fig.  36. — Section  of  fertilization  stage,  showing  deep  entrance  pit  of  a  sperm.     From  the  lowermost  point  arise  branching  rays. 

Fig.  37. — Detail  of  section  of  specimen  shown  in  fig.  34.  From  the  path  of  a  sperm  astral  rays  branch  in  many  directions,  and  at 
various  points  (indicated  by  the  dark  points)  new  centers  of  radiation  appear. 

Fig.  38. — Detail  of  fertilization  stage  shown  in  fig.  34.  The  present  section  follows  almost  exactly  the  entrance  path  of  a  sperm.  The 
latter  appears  at  .v,  and  it  is  seen  that  the  entrance  pit  is  a  delicate  tube  extending  downward  in  the  direction  of  a  sperm.  Around 
the  latter  appears  a  well-marked  aster,  and  in  this  neighborhood,  strung  along  a  prominent  ray  of  the  aster,  are  a  number  of  deeply 
stained  "  centrosomes."  A  similar  "  centrosome  "  occurs  near  the  lowermost  point  of  the  entrance  tube  of  the  sperm. 

forming  a  plug-shaped  mass  twice  as  deep  as  wide  (fig.  34).  This  is  possibly  the 
homologue  of  the  Panderian  nucleus  figured  in  the  shark  egg ;  certain  it  is,  how- 
ever, that  the  egg  of  Chimaera  has  not  as  clearly  a  marked  series  of  tunics  in  its 
yolk  arrangement. 


THE  EGG  AND  ITS  MEMBRANES. 


47 


THE  GERMINAL  VESICLE. 

This  is  eccentric  in  eggs  even  as  small  as' 3  mm.  (cf.  fig.  30).  In  the  section  of  a 
well-grown  ovarian  egg  shown  in  fig.  33  it  lies  close  to  the  side  of  the  egg.  The 
spireme  has  here  contracted  into  a  minute  mass  and  has  given  rise  to  (about)  twelve 
pairs  of  chromosomes.  *  These  are  of  remarkably  small  size,  smaller  by  about 
one-half  than  those  of  a  corresponding  stage  of  shark  (Pristiurus);  and  they  are 
also  smaller  in  terms  of  the  germinative  vesicle.  In  Pristiuris  (Riickert)  the  mass  of 
chromosomes  at  this  stage  measures  36  p  in  width  and  the  vesicle  296  ;  in  Chimaera 

40 


39 


&£&?yi  :-:S3sjS 

'M 


Fig.  39. — Detail  of  sperm  nucleus  from  section  of  late  fertilization  stage.  The  sperm  head  is  surrounded  by  a  conspicuous  aster, 

in  some  of  whose  dendritic  rays  appear  the  nodes  referred  to  below.     The  sperm  nucleus  itself  is  undergoing  amitotic 

division.      X  475. 
Fig.  40. — Detail  of  section  of  late  fertilization  stage.      Throughout  the  germinal  yolk  occur  asters  which  have  no  apparent 

reference  to  nuclear  structures.     At  /  many  of  these  asters  appear  around  a  large  granule  of  yolk.     It  will  be  seen  that 

the  rays  are  formed  as  lines  in  the  thickened  walls  of  alveoles. 
Fig.  41. — Detail  of  section  of  late  fertilization  stage,  showing  asters  in  germinal  yolk. 
Fig.  42. — Detail  of  section  of  late  fertilization  stage.      At   n  the  egg-nucleus  is  shown  surrounded  by  a  number  of  asters. 

The  asters  appear  to  lack  centrosomes  and  centrosphere.     Note  as  before  rays  formed  from  rims  of  alveoles. 
Fig.  43. — Section  similar  to  the  foregoing.     A  sperm  nucleus,  however  (n).  is  shown  surrounded  by  asters. 

the  same  mass  measures  16  and  the  vesicle  570.  In  other  words,  with  a  germinal 
vesicle  twice  the  size,  the  size  of  the  chromatin  mass  in  Chimaera  is  but  one-half 
that  of  the  shark.  In  the  shark  the  chromatin  mass  measures  about  one-ninth  the 
diameter  of  the  vesicle;  in  Chimsera,  on  the  other  hand,  about  one  thirty-eighth. 
This  condition  indicates  again  the  greater  specialization  in  the  egg  of  Chimsera. 
The  chromosomes  themselves,  it  will  be  remarked  (figs.  33  c,  33  D),  vary  considerably 
in  length  ;  thus  the  pair  shown  at  x  are  apparently  longer  than  those  at  y  and  at  2, 
and  a  detailed  examination  has  convinced  the  writer  that  this  difference  is  a  real 
one,  i,  c. ,  not  due  to  the  oblique  position  of  the  objects.  This  observation  may  be 
mentioned,  since  it  affords  an  additional  suggestion  as  to  the  individuality  of  the 
chromosomes,  recently  discussed,  e.  g.,  by  Sutton,  Wilson,  and  Moenkhaus. 

*Preliminary  to  first  polar  division.     The  number  of  chromosomes  is  clearly  much  smaller  than  in  sharks  ( 36  in 
Pristiurus  and  Torpedo). 


CHIM^ROID   FISHES  AND  THEIR   DEVELOPMENT. 


FERTILIZATION. 


Fertilization  begins,  as  in  sharks,  in  the  uppermost  portion  of  the  oviduct  and 
continues  throughout  the  period  of  the  formation  of  the  capsule.*  The  earliest 
stage  in  the  writer's  material  was  obtained  from  a  capsule  like  that  shown  in  plate  in, 
fig.  1 3,  earlier  stages  not  having  been  handled  successfully.  Late  stages  were  secured 


4.6  A 


45 


454 


46 


••:-.'•  .- 


91 


-•  "•  .  u-'   v 
•  v.  '' 


Fig.  44. — Detail  of  late  fertilization  stage,  showing  male  nucleus  in  the  process  of  approaching  the  egg  nucleus.    A  club-shaped  centrosome 

surrounded  by  astral  rays  appears  at  (right)  side  of  nuclear  membrane.     X   475. 

Fig.  45. — Detail  of  section  similar  to  the  last.     A  well-marked  vacuole  (artifact?)  appears  at  one  end  of  nucleus. 
Fig.  45A. — Sperm  nucleus  with  aster  from  section  similar  to  the  preceding. 

Fig  45B. — Sperm  nucleus  from  stage  similar  to  foregoing.     The  center  of  aster  is  to  be  found  in  the  section  below  present  one. 
Fig.  46. — Detail  of  section  shown  in  fig.  34.       Sperm  nucleus  has  divided  amitotically.      This  at  first  suggests  a  stage  of  copulating 

pronuclei. 

Fig.  46A. — Egg  and  sperm  nuclei  in  apposition.     Rays  not  conspicuous. 

Fig.  47. — Early  prophase  of  segmentation  nucleus.     Two  asters  are  present,  one  of  which   (the  right)  contains  two  centrosomes. 
Fig.  47 A. — Early  segmentation  stage.     Section  passing  through  segmentation  nuclei.     No  surface  furrows  are  as  yet  present.     X  190. 

from  capsules  about  as  shown  in  plate  in,  fig.  16.     In  the  present  account  the 
stages  may  conveniently  be  referred  to  as  early,  middle,  and  late. 

An  early  stage  is  shown  in  surface  view  in  plate  iv,  fig.  18,  magnified  about 
15  diameters.  This  was  drawn  from  a  living  egg  and  shows  the  germinal  area 
somewhat  misshapen,  due  to  rupture  of  the  vitelline  membrane,  f  The  germinal 
area  is  not  sharply  outlined  ;  it  is  the  same  color  as  the  remainder  of  the  egg,  and 

*  The  egg  at  deposition  is  undergoing  the  first  stage  of  segmentation. 
\  This  is  conspicuous  at  this  stage,  glossy  and  tense. 


FERTILIZATION   STAGES.  49 

is  only  demarked  by  a  slight  furrow.  Under  a  dissecting  lens  a  number  of  minute 
depressions  indicate  the  points  of  entrance  of  sperms.  Seven  of  such  points  appear 
in  the  present  instance,  and  all  of  them  are  peripheral;  four  are  close  together.  In 
this  case  sections  show  that  no  sperms  have  entered  the  middle  of  the  germ. 

A  middle  stage  in  fertilization  (plate  iv,  fig.  19),  also  examined  in  the  living  egg, 
showed  23  entrance  pits.  Of  these  half  a  dozen  are  of  large  diameter  and  several 
are  minute,  a  condition  which,  in  comparison  with  the  preceding  stage,  suggests 
that  the  small  pits  are  the  early  phases  of  the  large  ones,  and  we  query,  accord- 
ingly, whether  in  point  of  time  the  entrance  of  sperms  in  Chimsera  may  not  prove  an 
extended  process  (v.  infra,  heading  /).  In  the  present  specimen  it  will  be  seen 
that  the  sperms  have  entered  not  only  the  germinal  substance  but  the  bottom  and 
even  the  outer  wall  of  the  germinal  fosse. 

Study  of  sections  leads  us  to  conclude: 

(a)  That  the  tail  of  the  spermatozoon  does  not  enter  the  egg.     In  fig.  35   a 
sperm   is   shown  which  has  just   entered  the   egg ;    the  middle  piece,   mp,   ends 
abruptly,  and  there  is  no  trace  of  the  tail.     The  entrance  pit  is  not  yet  sharply 
formed. 

(b)  That  the  head  of  the  spermatozoon  rotates  as  it  travels  inward.     Even  at 
the  early  period  above  figured,  the  filamentous  character  of  the  sperm  head  has 
been  lost ;  it  is  now  spheroidal,  surrounded  by  a  light-colored  area  of  the  germ. 
Although  hardly  within  the  egg,  its  axis  inclines  45°  to  the  surface,  and  its  middle 
piece  is  parallel  with  the  surface,  a  condition  which  by  analogy  with  other  forms 
leads  us  to  conclude  that  it  has  already   begun  a  process  of  rotation.      In  a  later 
stage  in  the  entrance  of  the  sperm  (fig.  38)  the  lighter-colored  portion  of  the  "  head  " 
points  toward  the  surface  of  the  germ  and  thus  indicates  that  the  rotation  has  been 
carried  through  an  angle  of  180°. 

(c)  A  state  of  remarkable  kinetic  activity  exists  in  these  stages.      In  fig.  36  a 
series  of   "astral  rays"  are  seen  diverging  downward  from  the  entrance  pit  of  a 
spermatozoon  (cf.  the  observations  of  Miss  Foote  in  Allolobophora).    And  from  paths 
traversed  by  a  sperm  "astral  rays"  arise,  sometimes  radiating  regularly,  but  usually 
branching  irregularly  and  forming  new  groups  of  radiation.     At  such  points  of 
reradiation  darkly  staining  bodies  occasionally  appear  which  remind  one  of  centro- 
somes.     In  the  present  fig.  34  branching  astral  rays  are  seen.     These,  it  is  found, 
have  arisen   around  a  sperm   path.     A  similar  series  greatly  enlarged  is  shown 
in  fig.  37,  a  series  of  considerable  interest,   since  it  shows  many   "centrosomes" 
surrounded  by  bending  and  irregularly  branching  rays.      The  "centrosomes"  some- 
times appear  at  centers  of  reradiating  rays  in  sperm  asters  (figs.  38,  39);  at  other 
times  they  arise  without  any  apparent  relation  to  sperm  asters  or  sperm  paths,  as 
around  an  unusually  large  yolk  granule  (fig.  40,  the  group  at  the  right).     As  shown 
in  the  last  figure,  more  than  half  a  dozen  centers  of  radiation  appear  around  the 
yolk  granule.      On  the  other  hand,  the  two  large  "asters"  shown  at  the  left  in  the 
present  figure  have  no  apparent  relation  with  the  former  series,  nor  are  they  in  the 


-0  CHIM^EROID   FISHES  AND  THEIR  DEVELOPMENT. 

neighborhood  of  sperm  asters.  A  similar  pair  of  "asters"  are  shown  in  fig.  41, 
On  the  other  hand,  the  asters  shown  in  fig.  42  are  arranged  around  the  male 
pronucleus,  but  how  they  are  related  to  one  another  can  not  safely  be  inferred.  In 
the  following  section  (fig.  43),  drawn  from  the  same  specimen,  a  similar  radiation 
occurs  around  a  supplemental  sperm  head,  n.  In  the  four  preceding  cases  it  is 
interesting  to  observe  how  perfectly  the  rays  fulfil  the  alveolar  conditions  for  aster 
formation  as  explained  by  Biitschli.  Note  in  this  connection  the  large  size  of  the 
alveoli  in  the  immediate  neighborhood  of  the  aster. 

(ct)  The  behavior  of  the  germ  nuclei  in  fertilization  is  similar  to  that  in  shark. 
The  sperm  which  enters  the  germ  in  the  region  nearest  to  the  egg  nucleus  is  the  one 
which  accomplishes  fertilization;  it  undergoes  the  customary  form  changes  while 
traveling  through  the  germ.  In  the  stage  shown  in  fig.  44  its  chromatic  material 
is  becoming  resolved,  and  the  aster  which  appears  beside  it  radiates  from  a 
centrosome,  which  is  in  this  case  somewhat  elongated,  situated  close  to  the 
nuclear  membrane.  A  stage  somewhat  earlier  than  the  foregoing  is  shown  in  fig. 
45 ;  this,  however,  represents  a  stage  in  the  development  of  a  supplemental  sperm 
head.  The  foregoing  figures  are  taken  largely  from  late  stages  in  fertilization.  A 
stage  from  a  nearly  finished  capsule  (fig.  46)  pictures  the  union  of  the  germ  nuclei, 
i.  e.,  corresponding  to  Ruckert's  fifth  stage  in  the  fertilization  of  the  ray  (Torpedo), 
as  figured  in  the  Kupffer  Festschrift  (fig.  53  B).  On  the  other  hand,  fig.  46  A, 
which  at  first  sight  suggests  copulating  pronuclei,  must  be  construed  as  picturing  a 
(sperm)  merocyte  dividing  amitotically;  for  here  a  third  nucleus  is  found  to  be  pres- 
ent, above  the  niveau  of  the  other  two.  The  figure  indicates,  further,  the  retention 
of  the  aster  and  an  extensive  pale-colored  area  surrounding  the  nuclei. 

(e)  The  behavior  of  the  supplemental  sperm  heads  is  also  notably  shark-like.  In 
even  the  middle  stage  of  fertilization  they  can  not  readily  be  distinguished  from  the 
early  sperm  nucleus.  Indeed,  the  nearer  they  are  in  a  position  to  the  egg  nucleus 
the  more  difficult  they  become  to  distinguish  from  one  another.  And  conversely 
those  undergo  the  least  conspicuous  changes  which  occur  in  the  margins  of  the 
germ.  We  have  already  referred,  in  fig.  45,  to  a  structure  which  from  its  position 
is  apparently  the  early  sperm  nucleus.  In  this  phase,  at  the  margin  of  the  nucleus 
is  a  vesicular  area,  at  one  end  of  which  an  aster  radiates  from  a  minute  centrosome. 
A  somewhat  similar  appearance  occurs  in  what,  from  its  eccentric  position,  is 
undoubtedly  a  supplemental  sperm  head  (fig.  45  A).  Here  the  vesicular  area  of 
the  nucleus  is  less  perfectly  developed,  strands  of  karyoplasm  passing  from  the 
nuclear  membrane  to  the  large  and  deeply  staining  mass  of  chromatin,  a  stage, 
indeed,  which  may  be  looked  upon  as  the  earlier  condition  of  that  of  fig.  45. 
Another  sperm  head  (fig.  45  B)  from  the  same  series  of  sections  is  intermediate 
between  those  of  figs.  45  and  45  A.  The  vacuolated  margin  is  now  broken  into 
several  discrete  areas,  and  the  chromatin  is  collected  into  a  diffuse  mass,  irregular 
in  outline.*  From  this  stage  the  transition  is  not  wide  to  that  of  fig.  34,  in 

*The  aster  lies  below  the  plane  of  the  section. 


FERTILIZATION    STAGES.  cr 

which  is  pictured  a  (sperm)  merocyte  occurring  eccentrically  (n)  in  the  germinal 
area  of  an  egg  twin  to  the  preceding.  In  this  the  vacuolar  area  has  been  practically 
lost,  the  aster  increased  in  size,  and  the  nucleus  subdivided  into  a  number,  probably 
five  or  six,  of  smaller  merocytes.  Division  of  this  kind  has  been  observed  in  many 
instances;  and  on  the  other  hand  no  case  has  been  found  in  which  a  sperm  nucleus 
divides  indirectly.  This  condition  is  noteworthy,  since  it  emphasizes  on  still 
another  line  the  specialization  of  the  Chimaeroid.  For  in  the  shark  the  sperm 
nuclei  may  undergo  indirect  division  throughout  practically  the  entire  process  of 
cleavage;  and  when  early  direct  divisions  do  appear,  e.  g.,  in  the  third  cleavage 
(Riickert  in  Torpedo),  they  still  show  traces  of  their  mitotic  ancestry.  Indeed,  the 
nearest  condition  to  the  presegmentation  division  of  the  sperm  head  in  Chimsera 
(fig.  39)  occurs  in  shark  only  in  the  period  of  later  segmentation  (cf.  Riickert,  op. 
cit.,  pi.  in,  fig.  1 8).  In  other  words,  the  morphological  (or  the  physiological) 
result  which  in  the  shark  is  effected  only  at  the  end  of  a  series  of  graduated  stages 
is  accomplished  by  Chimsera  at  a  single  stroke — a  condition  worthy  of  comment, 
since  it  affords  a  palpable  case  of  "precocious  segregation." 

(_/)  The  sperms  enter  the  germ  not  simultaneously,  but  during  a  relatively 
extended  period.  The  pits  formed  by  the  sperms  when  entering  the  germ,  as  already 
noted,  are  different  in  size,  and  we  accordingly  infer  that,  as  the  sperms  themselves 
do  not  differ  materially  in  size,  nor  in  all  probability  in  individual  activity,  the  dif- 
ference in  the  pits  is  due  to  their  having  been  formed  at  successive  periods.  This 
suggestion  is  borne  out  by  examination  of  sections.  Thus,  in  fig.  36  an  entrance 
pit  is  shown,  pointing  down  in  the  direction  of,  but  not  actually  connected  with,  a 
sperm  head  lying  deep  in  the  germ.  And  here  the  pit  or  funnel  has  a  wide  mouth. 
On  the  other  hand,  in  fig.  38,  a  funnel  is  pictured  whose  apex  is  still  connected 
with  a  sperm  head,  and  its  mouth  is  narrow.  The  sperm  head,  in  this  case,  lies 
in  a  shallower  layer  of  the  germ,  and  from  its  structure,  also,  is  clearly  a  younger 
stage  in  development.  It  follows,  therefore,  that  the  former  sperm  entered 
the  germ  at  an  earlier  period  than  the  latter,  and  that  the  process  of  semina- 
tion is  a  relatively  extended  one — relatively,  since  in  sharks  all  sperms  appear 
to  enter  simultaneously.  The  suggestion  may,  on  the  other  hand,  be  made  that 
the  difference  in  the  behavior  of  the  sperms  in  the  germ  might  be  due  rather  to 
their  location  than  to  their  time  of  entrance;  or,  in  other  words,  that  the  rapidity 
of  their  development  might  be  influenced  by  their  proximity  to  the  egg  nucleus. 
This  suggestion,  however,  is  not  tenable  in  view  of  the  condition  of  the  fertilization 
stage  (middle  stage)  shown  in  plate  iv,  fig.  19,  for  here  small  pits  occur  side  by  side 
with  large  ones,  both  in  the  middle  of  the  germinal  area  and  on  the  sides. 

Finally,  to  contrast  Chimsera  and  shark  in  stages  of  fertilization:  In  Chi- 
msera  the  entrance  of  the  sperms  is  a  protracted  process;  but  as  soon  as  the  sperms 
(other  of  course  than  the  one  which  fertilizes  the  egg)  enter  the  germ  they  divide 
promptly  by  amitosis,  with  the  very  probable  result  of  producing  a  greater  number 


tj2  CHIM^ROID   FISHES  AND  THEIR   DEVELOPMENT. 

of  merocytes  in  a  shorter  time.  *  It  thus  appears  that  the  early  divided  merocytes 
are  equivalent  morphologically,  and  probably,  therefore,  physiologically,  to  late 
merocytes  in  sharks.  Furthermore,  at  the  time  of  fertilization  the  number  of  sperms 
entering  the  egg  of  Chimsera  appears  to  be  greater  than  in  sharks.  The  average 
number  reckoned  by  Riickert  in  Pristiurus  is  about  16;  in  Chimsera  it  is  at  least 
24,  judging  from  the  number  of  entrance  funnels  in  late  stages  of  fertilization. 
Again,  in  Chimera  the  sperms  form  and  long  retain  definite  paths  in  the  germ  which 
are  unknown  in  other  forms;  so  also  are  their  entrance  funnels  more  conspicuous. 
The  sperm  nuclei,  furthermore,  as  well  as  the  segmentation  nuclei,  are  the  more 
special  in  terms  of  the  entire  egg,  since  they  are  smaller  than  in  sharks  (in  diameter 
about  one-half).  Also,  as  evidence  of  specialization — for  these  structures  have 
clearly  a  special  physiological  value — witness  the  great  number  of  asters  and  their 
ready  mode  of  appearance,  e.  g.,  around  vagrant  yolk  granules  of  extraordinary 
size.  In  point  of  histological  differentiation  of  the  germinal  cytoplasm,  finally,  we 
observe  in  Chimsera  conditions  unparalleled  in  the  shark.  We  recall  here  the  differ- 
entiation of  typical  Schaumplasma,  the  light  areas  surrounding  the  nuclei,  and  the 
extensive  development  of  astral  rays. 

SEGMENTATION. 

Drawings  of  the  living  germ,  plate  iv,  figs.  20-29,  give  a  general  idea  of  the 
process  of  segmentation.  And  in  surface  view  this  resembles  distinctly  the  usual 
conditions  in  shark.  There  is  the  same  type  of  germinal  area  in  which  cleavage  lines 
appear,  and  a  marginal  zone  which  apparently  circumscribes  the  area  of  cleavage. 

In  the  first  of  these  figures  the  germinal  area  appears  convex,  although  some- 
what flattened  above,  and  is  separated  from  the  surrounding  germinal  yolk  by  a 
narrow  fosse.  The  furrow  which  appears  to  traverse  it  is  sharpest  and  deepest  in 
the  middle  of  the  germ  and  fades  away  at  the  margins.  The  surrounding  zone  of 
germinal  yolk,  however,  extends  widely  over  the  surface  of  the  egg  and  lacks  a 
sharply  marked  outer  boundary  line.  Its  inner  boundary,  i.  e. ,  at  the  fosse,  shows 
a  number  of  small  eminences  These,  as  sections  also  show,  correspond  to  the 
eminences  formed  in  the  shark  blastoderm  by  peripheral  (sperm)  merocytes;  they 
are  more  numerous  at  the  corresponding  stage  and  are  more  regularly  disposed 
around  the  germ. 

In  further  detail:  Sections  of  the  present  specimen  demonstrate  that  in  spite 
of  the  single  apparent  furrow  the  present  stage  represents  not  the  first,  but  the 
third  cleavage,  two  cleavage  furrows  having  been  retarded  (?  suppressed),  for  there 
are  found  to  be  present  six  segmentation  nuclei.  This  condition,  it  may  be 
remarked,  occurs  in  certain  specialized  sharks  (Torpedo). 

The  first  division  of  the  segmentation  nuclei  is  accompanied  by  no  trace  of  a 
surface  furrow.  Such  a  stage  is  shown  in  fig.  47  A.  The  nuclei  are  here  somewhat 
widely  separated  from  one  another  and  are  in  the  resting  stage ;  the  only  indication 


*Recent  examinations  of  the  sections  of  the  fertilization  stage  which  yielded  fig.  46  A  (Chimaera  Emb.  12,  in  my 
cabinet)  show  that  no  less  than  88  (sperm)  merocytes  are  present.  Thus  in  Chimaera  as  many  merocytes  are  present 
in  a  presegmentation  stage  as  in  Torpedo  (Ruckert)  in  a  stage  of  fourth  cleavage. 


SEGMENTATION  STAGES,  53 

of  cleavage  is  in  the  arrangement  of  the  germinal  cytoplasm  afotind  the  nuclei. 
This  is  expressed  in  such  a  way  that  the  germinal  yolk  rises  between  them  like  a  walL 
The  second  stage  in  which  cleavage  is  seen  at  the  surface  is  shown  in  plate  iv, 
fig.  21,  from  the  egg  companion  to  the  one  shown  in  plate  iv,  fig.  20,  but  incubated 
longer  (about  forty  minutes).  Here  a  second  furrow  is  noticeable.  The 
resulting  "  blastomeres  "  are  unequal  in  size,  one  of  them  being  as  large  as  two  of 


Fig.  48. — Section  passing  between   the  point  1  and  1  of  the  segmentation  stage  shown  in  PI.  IV,  fig.  20.     In  the  present  section  the 

line  which  appeared  to  indicate  first  cleavage  lies  below  the  point  f;  below  this  a  vacuole  is  present  whose  lateral  extent  gives  one 

the  impression  of  the  width  of  the  furrow  noted  in  surface  view.     X  35. 
Fig.  49. — Section  through  a  segmentation  stage  corresponding  to  PI.  IV,  fig.  22.     It  will  be  observed  that  some  of  the  cleavage  lines 

do   not    open  to  the  surface,  as  at  c.      On  the  other  hand,  one  of  the  spaces  between  the  blastomeres  opens  into  a  fissure-like 

vacuole,  a. 
Fig.  50. — Similar  section  of  early  segmentation  stage,  in  which,  as  at  n,  a  nucleus  appears  without  any  neighboring  cleavage  furrow. 

A  line  of  thicker  germinal  yolk  appears  in  its  place. 
Fig.  51. — Section  of  early  cleavage  stage  in  which,  when  viewed  from  the  surface,  deep,  fissure-like  vacuoles  appear  as  cleavage  lines. 

the  others.  As  in  the  companion  stage  the  furrows  fade  away  at  the  margin  of  the 
germinal  area,  and  this  is  again  surrounded  by  a  somewhat  regular  ring  of  merocyte 
eminences.  It  may  be  mentioned  that  these  characters  are  materially  modified, 
i.  e.,  as  far  as  surface  view  is  concerned,  when  the  egg  is  hardened,  e.  g.,  in  acetic 
sublimate.  And  in  sections  it  is  found  that  the  circumgerminal  fosse  and  merocyte 
eminences  disappear  and  what  was  interpreted  as  surface  furrows  in  the  living  egg 
appear  as  long  and  wide  vacuoles.  Thus  in  fig.  48,  a  section  transverse  to  the 


e A  CHIMjEROID   FISHES  AND  THEIR   DEVELOPMENT. 

first  cleavage  line  of  the  stage  of  plate  iv,  fig.  20,  the  fosse  will  be  seen  to  have  dis- 
appeared, and  the  line  which  indicated  cleavage,  so  conspicuous  in  surface  view, 
now  appears  under  the  point  /  as  a  vacuole  triangular  in  section,  its  apex  touching  the 
surface  of  a  germ.*  Vacuoles,  we  note,  are  abundant  in  early  stages;  several 
are  present  in  the  section  of  the  germ  just  referred  to,  and  from  their  arrange- 
ment they  suggest  the  division  of  the  germ  into  blastomeres. 

Three  stages  of  early  cleavage  are  shown  in  surface  view  in  plate  iv,  figs.  22, 
23,  and  24,  the  first  as  an  opaque  object,  drawn  from  the  living  egg,  the  second  and 
third  as  translucent  objects,  in  the  last  cases  the  germ  having  been  removed,  placed 
in  a  watch  glass,  and  examined  by  transmitted  light  during  the  process  of  fixation. 
In  these  three  preparations  there  is  considerable  irregularity  in  the  surface  charac- 
ters; in  the  first  the  margins  of  the  blastomeres  are  rounded,  in  the  others  angular; 
outwardly  they  appear  to  represent  fourth  and  fifth  cleavages;  in  section,  how- 
ever, single  ' '  blastomeres  "  are  sometimes  found  to  contain  several  segmentation 
nuclei.  It  was  observed  that  the  resting  and  dividing  nuclei  were  sometimes  found 
in  the  same  section,  and  it  follows  accordingly  that  in  Chimaera  the  synchrony  of 
cleavage  is  early  lost. 

Four  later  stages  of  segmentation  appear  in  plate  iv,  figs.  25,  26,  27,  and  28,  all 
drawn  under  conditions  of  transmitted  light,  the  living  specimens  having  been 
removed  and  examined  in  watch  glasses.  In  the  first  of  these  the  germ  is  well 
marked  off  from  its  circumgerminal  zone;  in  the  rest  some  of  the  marginal  cleav- 
age lines  were  traced  half-way  across  the  circumgerminal  zone,  and  in  a  few 
instances  these  lines  could  be  followed  quite  across  it.  In  these  stages  continued 
subdivision  of  the  "blastomeres"  has  taken  place,  those  in  the  central  position 
becoming  divided  oftener  than  those  near  the  periphery.  As  in  earlier  stages,  some 
of  the  cleavage  lines  are  probably  not  expressed  at  the  surface,  and  are  due  only  to 
vacuoles;  the  latter  are  lineal  in  surface  view,  sometimes  wide,  sometimes  narrow, 
occasionally  almost  attaining  the  surface,  at  other  times  lying  fairly  deep  in  the 
germ.  (Cf.fi.gs.  49,  50,51.)  Sometimes,  as  in  fig.  49,  they  are  actually  continuous 
with  cleavage  furrows,  as  at  a,  and  considering  the  relation  which  they  often  bear 
to  nuclei  (e.g.,  infra,  under  the  heading  "gastrulation"),  we  conclude  that  in 
some  cases — even,  indeed,  in  many  cases — they  are  homologous  to  cleavage  spaces, 
i.  e.,  that  they  are  cleavage  spaces  which  fail  to  become  expressed  at  the  surface 
of  the  germ.  This  conception  appears  to  be  applicable  even  when  the  vacuoles 
appear  in  the  peripheral  region  of  the  germ  in  fertilization  stages.  Thus  in  fig.  34 
the  masses  of  germinal  yolk  separated  by  the  vacuoles  (under  the  points  marked 
with  an  asterisk  [*])  usually  bear  sperm  nuclei  which,  as  we  know  by  analogy,  will 
cause  ' '  segmentation. "  Accordingly,  even  in  this  position  vacuoles  may  be  compared 
to  intercellular  spaces,  at  least  from  the  standpoint  of  developmental  mechanics. 

In  fig.  52  a  section  of  a  segmentation  stage  corresponding  to  plate  iv,  fig.  26, 
shows  that  cleavage  has  by  this  time  extended  deep  into  the  germinal  area.  Hori- 
zontal divisions  have  occurred,  irregularly  however,  for  in  some  places  the  blastoderm 

*There  is  thus  a  possibility  of  there  having  been  an  open  furrow  in  the  living  egg. 


CLEAVAGE  STAGES. 


55 


varies  in  thickness  from  one  to  five  cells.  Noteworthy  is  the  irregularity  of  the  yolk 
wall  out  of  which  blastomeres  are  segmenting,  as  at  x,  and  into  which  deep  inter- 
cellular spaces  are  continued,  becoming  confluent  below,  as  at  v,  v,  v,  with  vacu- 
oles  like  those  described  in  earlier  stages.  It  may  be  remarked  that  in  this  stage 
the  vacuoles  pass  deeply  into  the  yolk. 

Another  stage  of  late  segmentation  (or  blastula),  corresponding  in  general  with 
plate  iv,  fig.  27,  is  shown  in  the  series  of  sections,  figs.  53-56.  In  the  section,  fig.  53, 
which  passes  near  the  center  of  the  germ,  the  conditions  differ  little  from  the 
preceding  stage.  We  observe  that  continued  divisions  have  taken  place  and  that 
there  is  still  the  same  outcropping  of  blastomeres  from  the  yolk  wall,  as  at  .a:  and  x, 
following  mitoses.  An  advancing  character  in  this  stage  is  the  general  flattening  of 
the  germinal  wall,  as  at  the  point  y,  a  preliminary  step  toward  the  formation  of  the 
floor  of  the  segmentation  cavity,  and  possibly  indicating  fore  and  aft  differentiation 
of  the  germ.  It  may  be  remarked  that  this  is  the  first  stage  in  which  a  conspicuous 
zone  of  merocytes  was  seen.  These  are  numerous  under  the  central  blastomeres, 
most  numerous  under  the  peripheral  blastomeres,  and  then  rapidly  decrease  in 


^V.  :•;;: 

Fig.  52. — Section  of  late  cleavage  stage  (corresponding  to  PI.  IV,  fig.  26).      x.  Mass  of  germinal  yolk   from   which  a 
blastomere  is  being  budded  out ;  ?',  vacuoles  which  are  continuous  with  intercellular  spaces. 

number  peripherad.  The  three  sections,  figs.  54-56,  illustrate  such  a  series.  The 
first  of  them,  fig.  54,  indicates  the  relation  of  the  above-mentioned  vacuoles  to 
intercellular  spaces,  as  at  the  points  marked  with  an  asterisk  (*) ;  the  second  and 
third,  figs.  55,  56,  are  instructive  as  showing  the  extension  of  a  nest  of  cells,  n 
(it  is  the  same  group  in  both  sections — it  appears,  however,  at  the  left  in  the  lower 
section,  since  this  has  been  turned  over  on  the  slide),  beyond  the  margin  of  the 
circular  mass  of  blastomeres — instructive,  since  it  suggests  that  the  outlying 
region  of  the  germ  (circumgerminal  zone)  is  still  little  different  from  the  germ 
itself  in  its  cell-forming  nature.  It  is  also  to  be  observed  that  deep  fissures 
representing  intercellular  spaces  (fig.  56,  2),  extend  peripherad  through  the 
germinal  yolk,  corresponding  to  the  marginal  furrows  described  in  the  eggs  of 
ganoids  and  dipnoi,  of  Heterodontus,  even  of  amphibia.  There  is  here  accord- 
ingly a  region  in  which,  side  by  side,  occur  small  blastomeres,  large  yolk  masses 
(bearing  nuclei),  and  undivided  yolk  ;  there  is  no  gradual  transition  from  the  yolk 
to  the  large  blastomeres  and  from  these  in  turn  to  the  small  ones,  which,  as 
we  have  seen,  correspond  in  size  with  blastomeres  of  the  center  of  the  germinal 
area.  We  observe,  furthermore,  that  the  small  blastomeres  arise  in  any 


FISHES  AND  THEIR  DEVELOPMENT. 


neighboring  position,  as  in  figure  55,  at  a,  b,  or  c,  budding  out  directly  from 
the  yolk.  In  such  cases  the  important  question  remains  whether  the  nuclei 
which  pass  into  the  blastomeres  are  derived  from  segmentation  nuclei  or  from 


53 


%*&%$•?'$&*. 


55 


.SSSa^. 


-\         c 

J  .-•  -"55, -gffi;^^?SB^ 


Figs.  53-56.— Sections  of  late  segmentation  or  early  blastula  stage  (corresponding  to  PI.  IV,  fig.  27).  The  first  section  traverses  the 
mid-region  of  the  segmented  area,  the  others  progress  marginalward.  x,  Blastomeres  which  have  recently  budded  out  of  the  yolk  ; 
y,  wall  of  sub-germinal  yolk ;  z,  cleavage  line  passing  deep  into  the  sub-germinal  yolk  ;  *.  vacuoles  which  come  to  the  surface  of  the 
germ  and  form  intercellular  spaces.  X  35. 

sperm-nuclei.  In  the  latter  event,  judging  by  analogy,  they  would  show  amitoses 
only;  in  the  former  they  should  multiply  by  mitosis.  Examined  in  this  light  it 
is  found  that  the  nuclei  which  here  pass  into  the  blastomeres  show  amitoses,  and 


THE   DIVISION   OF  THE  YOLK.  57 

they  might  thus  be  regarded  as  of  sperm-head  origin.  On  the  other  hand,  it 
might  still  be  claimed  that  the  nuclei  of  such  blastomeres  were  derived  from  the 
segmentation  nuclei,  fora  more  careful  examination  shows  (i)  that  amitoses  exist 
in  the  blastomeres  in  the  central  region  of  the  germ,  and  (2)  that  no  mitoses  are 
found  in  the  zone  of  the  merocytes,  where  we  may  reasonably  expect  that  some 
nuclei  are  present  which  are  derived  from  segmentation  nuclei.  The  problem  is, 
nevertheless,  a  difficult  one,  and  hardly  to  be  answered  in  the  present  outline  of 
Chimsroid  development.  We  point  out,  however,  that  two  criteria  which  have  been 
given  a  prominent  place  in  the  discussions  of  sEafk  development  can  not  be 
employed  in  the  present  instance,  viz.  (i)  the  number  of  the  chromosomes  which 
would  naturally  give  a  clue  as  to  the  origin  of  the  nuclei  can  not  be  estimated  in  the 
merocytes,  since  they  are  here  undergoing  only  amitotic  division ;  (2)  the  size  of  the 
present  merocytes  can  not  prove  an  important  element  for  comparison,  since  they 
range  from  minute  to  large,  and  in  shape  from  spherical  to  greatly  elongated  and 
irregular. 

An  important  phase  of  the  cleavage  in  Chimaera  has  naturally  been  introduced 
by  the  foregoing  discussion,  i.  e.,  as  to  the  segmentation  of  the  egg  in  its  extra- 
germinal  region.  We  have  seen  that  as  segmentation  progresses  nuclei  (whether 
segmentation  or  sperm-merocyte)  spread  peripherad.  Their  presence  can  be 
determined  in  sections  ;  and  in  surface  view,  in  the  later  stages,  e.  g.,  plate  iv, 
fig.  28,  cleavage  lines  can  be  seen  passing  outward  in  the  region  of  the  circum- 
germinal  zone.  That  these  lines  are  actual  furrows  is  shown  in  such  a  section  as 
that  of  fig.  56  (at  the  right).  Such  marginal  furrows,  however,  are  usually  minute 
in  size,  and  are  often,  in  surface  view  at  least,  difficult  to  follow,  a  difficulty  which 
may  be  due  either  to  the  blending  of  these  delicate  lines  with  the  color  of  the 
circumgerminal  zone,  or  to  the  partial  or  total  confluence  of  the  adjacent  rims  of 
the  cleavage  furrows,  e.  g.,  as  in  the  marginal  blastomeres  of  Cryptobranchus 
(according  to  Ishikawa).  The  distinctness  of  these  lines,  however,  increases  after 
the  circumgerminal  zone  is  passed,  and  they  later  give  rise  to  what  we  must  regard 
as  the  most  remarkable  feature  of  the  segmenting  egg. 

To  follow  this  process:  In  fig.  57  a  late  stage  of  segmentation  is  shown;  the 
germ  is  atg;  nearby  are  nests  of  blastomeres  (cf.  fig.  56,  «),  two  of  which  are  of 
such  size  as  to  appear  in  the  figure,  as  at.^';  from  the  germ  radiate  furrows,  two  of 
which,  a  and  a',  have  become  conspicuous  at  the  periphery  of  the  egg,  where  they 
may  have  merged  with  similar  furrows,  or  indeed,  on  the  other  hand,  there  is  a 
possibility  that  the  long  furrow  passing  between  the  points  marked  with  an  asterisk 
(*)  may  be  the  deflected  continuation  of  the  lines  a  and  a'. 

In  figs.  58  and  59  furrows  are  seen  arising  from  or  near  the  circumgerminal 
zone,  and  examination  shows  they  deepen  as  they  proceed  peripherad.  In  the  egg 
shown  in  fig.  59  the  outgoing  line  subdivides  and  marks  out  superficially  a  narrow 
segment  of  yolk.  In  the  same  egg,  but  in  the  anterior  region,  we  note  another 
marginal  line,  b.  Examined  from  below  this  stage  is  of  considerable  interest 


_8  CHIM;EROID  FISHES  AND  THEIR  DEVELOPMENT. 

(fig.  60),  for  it  shows  that  while  the  cleavage  lines  have  failed  to  express  themselves 
on  the  dorsal  side  of  the  egg,  they  yet  appear  conspicuously  on  the  vegetal  side.  Thus 
the  line  in  fig.  59  at  a  passes  sharply  inward  (fig.  60),  subdividing  into  a  series  of 

57  58 


Figs.  57-61.—  Eggs  showing  progressive  cleavage  of  the  yolk  mass.     In  a  blastula  (57)  a  conspicuous  fissure 

it  noted  between  the  points  *  and  *. 


cleavage  lines  which  in  turn  merge  with  other  cleavage  lines  (b-g) 
passing  downward  and  inward  from  the  equatorial  zone  of  the  egg. 
In  some  cases  well-marked  yolk  masses  are  outlined,  as  at  the  point 
marked  with  an  asterisk  (*),  suggesting  large  yolk-filled  blasto- 
meres  on  the  ventral  wall  of  an  amphibian  blastula.  It  may  be 
remarked  that  the  lines  here  described  are  not  mere  surface  mark- 
ings, for  during  the  process  of  hardening  an  egg,  e.  g.,  in  acetic- 
sublimate,  one  may  separate  the  yolk  masses  by  aid  of  dissecting 
needles,  and  in  this  process  it  becomes  clear  that  the  lines  are  in 
reality  fissures  dipping  deeply  into  the  substance  of  the  egg. 
Indeed,  in  the  former  specimen  it  was  found  that  the  mass  marked 
with  an  asterisk  (*)  could  be  removed  en  bloc  from  the  remaining 
mass  of  yolk.  It  is  evident,  accordingly,  that  in  this  stage  the  egg 
is  being  divided  up  on  its  ventral  side  into  a  number  of  large  yolk 
masses;  that  these  masses  stand  in  relation  to  the  entire  egg  very  much  as  do, 
e.  £-.,  in  the  frog's  egg,  the  blastomeres  of  the  lower  pole  to  this  entire  holoblastic 
egg  ;  further,  that  the  fissures  which  accomplish  this  result,  like  cleavage  lines  on 
the  vegetal  side  of  the  holoblastic  egg,  are  interconnected  with  a  series  (a-g,  in 
fig.  60)  of  cleavage  lines  which  pass  downward  and  inward  from  different  points  in 
the  equatorial  region  of  the  egg.  Between  the  stages  shown  in  figs.  59  and  60,  and 
those  in  figs.  61  and  27,  which  are  older  by  about  nine  days,  observations  are 
lacking.  It  is  nevertheless  clear,  by  comparison  of  these  stages,  that  the  yolk 
masses  shown  in  fig.  60  have  separated  from  one  another  widely  as  the  fissures 
deepened,  and  that,  as  the  masses  became  more  distinct,  their  condition  of  surface 
tension  —  in  view  always  of  the  syrupy  consistency  of  the  egg  —  caused  them  to 
round  out  their  contours  to  the  degree  shown  in  fig.  61. 


THE  DIVISION  OF  THE  YOLK.  59 

* 

In  dorsal  view  the  latter  stage  shows  few  large  yolk  masses,  and  these  are 
distinct  from  one  another,  although  closely  pressed  together.  The  yolk  masses, 
it  may  be  mentioned,  were  removed  separately  (in  the  living  condition)  without 
causing  their  rupture,  and  it  was  then  seen  that  the  fragmentation  of  the  yolk  mass 
had  progressed  further  than  was  at  first  evident,  for,  lying  below  and  on  either 
side,  against  the  ventral  wall  of  the  capsule,  were  many  small  masses  of  yolk  (cf. 
fig.  61,  at  the  right,  and  fig.  27,  somewhat  behind  the  embryo),  their  contours 
rounded  out  for  the  most  part;  but  a  thick,  creamy  or  syrupy  fluid  in  which  they  lay 
made  it  further  evident  that  in  some  cases  the  yolk  masses  had  broken  down. 
This  fluid,  we  remark,  was  observed  in  specimens  of  this  stage  only  when  the 
larger  masses  were  separated;  but  if  sea-water  was  injected  (by  pipette)  between 
the  larger  masses  as  they  lay  in  the  open  capsule,  it  would  dissolve  the  underlying 
creamy  yolk  and  the  entire  contents  of  the  capsule  would  become  hidden  from 
sight  in  the  resulting  milky  fluid. 

One  might  conveniently  digress  at  this  point  to  follow  the  fate  of  the  yolk 
masses  above  mentioned.  The  blastoderm  appropriates  only  a  small  portion 
(which  has  been  estimated  as  about  one-tenth  of  the  volume)  of  the  entire  egg. 
This  separate  yolk  mass  is  shown  slightly  shaded  in  figs.  27  and  61,  and  the  blasto- 
derm, with  its  attached  embryo,  has  as  yet  inclosed  only  a  small  portion  of  it.  A 
similar  stage  is  figured  in  plate  vin,  fig.  47,  and  a  somewhat  later  one  in  plate  viu, 
fig.  48.  In  the  latter  the  blastoderm  is  seen  to  have  almost  inclosed  the  yolk. 
It  completely  incloses  the  yolk  and  forms  a  diminutive  yolk  sac  in  the  embryo 
shown  in  plate  vin,  fig.  49,  and  a  similar  condition  occurred  in  the  embryo  of 
plate  ix,  fig.  50.  These  features  are  dwelt  upon  in  order  to  show  that  the 
behavior  of  the  blastoderm  in  appropriating  but  a  portion  of  the  yolk  is  a  normal 
phenomenon.  And  I  note  that  the  condition  shown  in  fig.  61  has  been  observed 
on  three  occasions  by  myself,  and  that  similar  conditions  were  recorded  by 
Dr.  Wilbur.*  In  supplementary  evidence  upon  this  point  we  may  again  refer  to 
the  embryo  of  plate  vin,  fig.  49,  for  in  this  the  yolk  sac,  although  of  miniature  size, 
is  evidently  normal,  since  it  exhibits  a  well-developed  vitelline  circulation,  f 

The  yolk-masses  other  than  that  appropriated  by  the  blastoderm  undergo  con 
tinued  subdivision.  This  is  in  progress  in  fig.  61,  where  the  large  yolk  mass  shown 
in  the  lower  part  of  the  figure  is  being  divided  into  three  smaller  ones.  We  have 
already  referred  to  the  pasty  fluid  present  among  the  lowermost  yolk  masses  in  this 
stage.  In  the  egg  capsule  from  which  the  embryo  of  plate  vin,  fig.  49,  was  taken, 
no  extra  embryonic  yolk  masses  were  found,  but  the  egg  capsule  contained  a  fluid  so 
cream-like  as  to  conceal  completely  the  embryo  and  lead  me  to  infer  that  the  egg 
was  addled,  almost  causing  me  to  throw  away  this  valuable  stage.  We  can  only 
conclude,  therefore,  that  the  creamy  fluid  was  due  to  the  continued  breaking  down 


*In  his  early  letters  Dr.  Wilbur  referred  to  these  conditions  doubtfully;  he  was  then  "not  sure  whether  they 
represented  normal  appearances." 

fTheyolk  sac  measured  about  half  an  inch  in  length  and  a  quarter  of  an  inch  in  breadth;  accordingly  at  this 
stage  of  development  it  represents  but  about  one-tenth  the  volume  of  the  egg  of  an  Elasmobranch  of  similar  size 
(e.  g.,  Spinax  niger}. 


60  CHIM;EROID  FISHES  AND  THEIR  DEVELOPMENT. 

of  the  yolk  masses  of  the  earlier  stage.*  That  this  fluid  was  nutritive  to  the 
embryo  was  also  evident,  since  the  external  gills  were  dilated  at  various  points 
with  brilliantly  colored  blood  knots,  and  in  these,  as  I  later  found,  numerous 
erythrocytes  were  undergoing  division.  And  this  condition  in  the  gill  filaments 
is  the  more  clearly  correlated  with  the  presence  of  the  milky  fluid,  since  in  similar 
egg  capsules  (sharks  and  rays),  where  this  milky  fluid  mass  is  lacking,  blood  knots 
on  the  external  gills  are  also  absent.  One  infers,  moreover,  that  the  milky  fluid, 
which  from  its  included  yolk  is  highly  nutritive,  may  also  be  passed  as  food  into 
the  mouth  of  the  embryo  and  assimilated  in  the  gut.  But  to  this  I  will  refer  at  a 
later  point. 

The  entire  process  of  the  fragmentation  of  the  egg  of  Chimaera,  it  will  be  seen, 
is  worthy  of  especial  comment.  Unlike  the  eggs  of  other  vertebrates,  and  unlike, 
indeed,  those  of  invertebrates,  unless  we  include  a  somewhat  generic  resemblance 
in  certain  mollusks  (e.  g.,  Neritina,  Blochmann,  1887)  and  in  certain  digenetic 
trematodes,  the  present  egg  follows  in  its  development  two  distinct  paths,  i.  e.,  a 
small  portion  of  the  egg  develops  in  the  direction  of  producing  the  embryo  with 
its  complete  though  diminutive  yolk  sac;  the  remaining  portion,  about  nine-tenths 
of  the  bulk  of  the  egg,  proceeds  to  undergo  a  process  of  repeated  fragmentation  to 
the  end  that  it  may  be  appropriated  by  the  embryo  secondarily. 

To  account  on  phyletic  grounds  for  this  extraordinary  and  "unnatural"  plan  of 
development,  one  must,  I  believe,  start  with  the  premise  that  the  fragmentation 
of  the  egg  is  a  process  comparable  with  total  cleavage.  This  premise  we  may 
accept  on  the  following  evidence: 

(1)  The  fragmentation,  like  cleavage,  is  progressive. 

(2)  Although  the  cleavage  lines  have  never  been  followed  conclusively  from 
the  rim  of  the  blastoderm  into  the  deep  fissures  which  initiate  the  fragmentation, 
they  have  at  least  been  observed  in  late  stages  of  segmentation  to  pass  out  over  the 
circumgerminal  zone  in  the  direction  of  the  peripheral  fissures  (cf.  in  this  regard 
the  evidence  of  Heterodontus).f 

(3)  The  yolk  masses  give  evidence  of  being  nucleated.     There  is  in  the  first 
place  evidence  that  the  nuclei  travel  peripherad.     In  the  stages  of  plate  iv,  figs. 
25-27,  nuclei  are  found  to  have  occupied  the  circumgerminal  zone,  i.  e.,  they  have 
traveled  outward  a  distance  equal  to  about  three-quarters  of  the  diameter  of  the 
blastoderm.     In  an  early  gastrula,  furthermore  (plate  v,  fig.  31),  and  in  section, 
fig.  63,  they  have  proceeded  outward  a  distance  equal  to  twice  the  diameter  of  the 
blastoderm.      Now,   on  the  evidence  of  progressive  centrifugal  movement  of  the 

*The  reader  may  reasonably  query  at  this  point  how  it  happens  that  the  creamy  nutritive  material  is  not  washed 
out  through  the  openings  of  the  capsule  during  the  respiration  of  the  young.  This  result  has,  I  take  it,  been  avoided 
in  the  course  of  the  evolution  of  this  process  in  two  ways  :  (i)  By  retarding  the  appearance  and  growth  of  the  capsular 
openings  until  the  nutritive  material  is  partly  consumed ;  (n)  by  the  great  density  of  the  creamy  fluid,  for  if  the 
nutritive  fluid  be  heavy  (and  experiments  with  the  living  eggs  have  convinced  me  that  this  is  the  fact),  a  moderate 
current  of  sea-water  could  be  passed  over  it  without  causing  it  to  be  washed  away. 

tAnnot.  Zool.  Jap.,  1901,  vol.  iv,  pt.  I,  pp.  1-7. 


THE  REDUCED  SIZE  OF  THE  YOLK  SAC.  6 1 

nuclei,  and  as  this  nucleated  area  (in  diameter)  is  measurably  greater  than  that 
of  the  yolk  mass  which  the  blastoderm  comes  to  inclose,  it  follows  that  nuclei  are 
present  in  some  of  the  outlying  yolk  masses.  Of  this,  however,  we  must  none  the  less 
admit  that  no  direct  proof  is  at  hand,  since  no  sections  of  these  outlying  yolk  masses 
were  made.  In  this  connection  I  observe  that  if  the  embryo-bearing  yolk  mass 
be  examined  even  under  a  low  power  (plate  viu,  fig.  480)  one  obtains  a  fairly  con- 
vincing picture  of  its  holoblastic  character. 

(4)  The  foregoing  evidence  is  none  the  less_strong  if,  conversely,  we  consider 
that  on  no  other  morphological  ground,  save  that  of  cleavage,  using  the  word  in  a 
broad  sense,  can  this  progressive  and  normal  fragmentation  be  explained. 

Accepting,  then,  the  premise  that  these  divergent  paths  in  the  development 
of  the  egg  of  Chimera  took  their  origin  in  a  holoblastic  egg,  the  present  con- 
ditions may  well  have  been  developed  on  somewhat  the  following  lines :  In 
the  primitive  Chimseroid  the  egg  resembled  that  of  Cestraciont;  it  was  probably, 
however,  not  as  large  as  that  of  the  recent  Heterodontus,  but  its  cleavage  fissures 
were  deeper  and  more  numerous.  The  embryo  at  that  stage  had  the  usual 
external  gills  of  the  selachian.  The  next  stage  would  be  attained  when  the 
gill  filaments,  passing  beyond  the  stage  of  the  well-known  trophonemata,  came  to 
appropriate  the  white  of  the  egg  which  was  contained  in  the  deep  cleavage  fissures, 
a  process  which  in  time  caused  or  accompanied  («)  the  deepening  of  the  fissures, 
and  in  further  time  (fr)  a  rupture  at  the  bottom  of  the  fissures.  Through  such  a 
process  yolk  material  came  to  escape  and  mingle  with  the  albuminous  contents  of 
the  deep  fissures.  Such  a  process,  we  may  now  assume,  was  naturally  followed  by 
adaptative  changes  in  the  trophonemata,  which  in  the  end  accelerated  the  growth 
and  differentiation  of  the  embryo.  In  short,  at  this  evolutional  stage  the  embryo 
was  receiving  through  a  (morphologically)  indirect  channel  an  amount  of  nutri- 
ment which  rivaled  that  derived  from  the  vitelline  circulation.  The  result  was 
what  one  would  have  anticipated,  i.  e.,  the  down  growth  of  the  vascular  blastoderm 
was  retarded,  while  the  fissuring  of  the  yolk-mass  became  deepened  and  the 
trophonemata  further  modified.  The  line  of  evolution  thus  carried  on  in  the  egg 
will  be  seen  to  involve  the  fate  of  the  yolk  sac,  viz. ,  in  determining  how  great  an 
amount  of  the  yolk  could  be  diverted  from  it.  In  the  present  species  (C.  colliei) 
about  nine-tenths  of  the  egg  has  been  diverted,  while  in  the  Callorhynchids,  where 
the  yolk  sac  is  known  to  be  larger,  possibly  not  more  than  half. 

In  the  foregoing  process  it  is  suggested  that  the  first  steps  in  the  disinte- 
gration of  the  yolk  mass  were  found  in  cleavage  phenomena.  It  should,  however, 
be  admitted  that  the  cleavage  may  not  have  been  equivalent  to  that  of  the  usual 
holoblastic  type.  The  nuclei  which  spread  peripherad  may  have  been  sperm-nuclei ; 
and  in  this  event  the  peripheral  furrows  are  special  phenomena,  unconnected, 
possibly,  in  phylogeny  with  the  cleavage  lines  in  the  holoblastic  egg.  Certainly 
in  favor  of  such  an  interpretation  is  the  fate  of  the  disintegrating  yolk  masses, 
since  such  a  fate  is  paralleled  somewhat  by  the  sperm-nuclei  in  the  shark  egg.  It 


62  CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 

is  opposed,  on  the  other  hand,  by  the  conditions  in  the  egg  of  Cestracion,  where 
the  peripheral  furrows,  similar  in  general  regards,  are  known  to  be  continuous  with 
those  of  true  cleavage.  The  question,  therefore,  can  not  be  answered  finally  until 
evidence  is  forthcoming  to  distinguish  the  kinds  of  nuclei  present  in  the  extra- 
embryonic  yolk  masses.  Meanwhile,  judging  at  least  from  the  behavior  of  the 
nuclei  in  the  circumgerminal  ring,  I  think  it  is  not  at  all  improbable  (cf.  Gastru- 
lation)  that  in  these  masses  both  sperm  and  segmentation  nuclei  are  present. 

Returning  again  to  the  development  proceeding  at  the  animal  pole  of  the  egg: 
We  recall  that  in  the  sections  figs.  53-56  there  was  shown  a  stage  of  late  seg- 
mentation, or  an  early  blastula,  such,  for  example,  as  pictured  in  plate  iv,  fig.  27. 
In  a  slightly  later  stage  (plate  iv,  fig.  28)  an  increased  number  of  blastomeres  are 
present,  and  there  is  still  an  indefinite  condition  in  the  periphery  of  the  germ, 
blastomeres  being  continued  irregularly  over  the  ring-like  circumgerminal  zone. 
On  the  other  hand,  in  plate  iv,  fig.  29,  a  stage  is  figured  earlier  than  the  preceding, 


Fig.  62. — Section  of  blastula.    sc,  Segmentation  cavity. 

but  showing  a  well-marked  line  of  demarcation  between  the  blastomeres  and  the  cir- 
cumgerminal zone.  It  seems  evident,  accordingly,  from  this  and  similar  instances, 
that  considerable  variation  occurs  as  to  the  time  at  which  the  marginal  relations  of 
the  germ  are  established.  Thus  in  the  stage  first  referred  to  (figs.  53-56)  the 
circumgerminal  zone  was  traversed  by  radial  fissures  and  invaded  by  nests  of  cells; 
in  a  similar  stage  (plate  iv,  fig.  29,  sectioned  in  fig.  62)  the  same  region  is  solid  and 
yolk-filled,  forming  a  compact  border  to  the  germ. 

In  contrasting  these  two  stages  one  observes  that,  while  they  can  differ  little  in 
point  of  age,  judging  from  the  number  of  blastomeres  in  the  cross  section  of  the 
middle  of  the  germ,  they  yet  have  marked  differences  in  their  relation  to  the  yolk ;  the 
former  has  around  it  and  under  it  "fine  yolk"  (Ruckert);  the  latter  has  its  fine  yolk 
contracted  into  a  thick  mass  lying  immediately  below  the  germ,  a  condition  which 
may  be  the  immediate  cause  of  the  failure  of  marginal  blastomeres  to  express 
themselves  in  a  peripheral  direction.  We  observe  that  in  fig.  62  the  fine  yolk  is 
pervaded  with  vacuoles  which,  from  their  shape  and  relations,  are  evidently  equiv- 
alent to  inter-blastomeral  spaces,  a  conclusion  which  is  supported  both  by  the 
nucleated  character  of  the  masses  of  fine  yolk  thus  outlined  and  by  the  continua- 
tion of  the  inter-blastomeral  spaces  with  the  distal  ends  of  the  vacuoles.  The  fine 
yolk,  in  short,  is  already  coming  to  be  formed  into  blastomeres,  and  it  is  interesting 
to  note  that  a  blastomere,  which  is  found  on  the  boundary  line  between  the  fine 


GASTRULATION.  g, 

and  coarse  yolk  is  composed  half  of  fine  and  half  of  coarse  yolk.  It  is  quite  prob- 
able, therefore,  even  from  this  single  observation  (cf.  also  infra),  that  the  region  of 
the  coarse  yolk  is  not  as  inert  as  one  is  at  first  inclined  to  believe,  an  induction 
which  suggests  at  once  that  the  fewer  and  larger  fissure-like  vacuoles  in  this  region 
are  equivalent  to  the  vacuoles  of  the  fine  yolk,  or  in  other  words,  to  intercellular 
spaces. 

A  final  point  of  contrast  between  the  foregoing  stages:  In  the  former  the 
blastomeres  are  relatively  compact;  in  the  latter  there-is  a  general  inter-blastomeral 
space  which  marks  an  early  state  of  the  definite  cleavage  cavity.  It  is  probable, 
as  noted  for  the  former  stage,  that  the  anterior  end  of  the  germ  can  now  be 


distinguished. 


GASTRULATION. 


The  stage  shown  in  surface  view  in  plate  v,  fig.  30,  and  in  sagittal  section  in 
fig.  63,  is  probably  the  most  valuable  of  the  author's  early  Chimaeroid  embryos. 
For  it  may  be  accepted  as  providing  a  key  to  the  problem  of  gastrulation  not  only 
in  this  form  but  in  sharks  as  well.  Its  discovery  is  none  the  less  a  fortunate  one, 
since  it  is  a  stage  which  has  every  appearance  of  being  brief,  and  therefore  easily 
overlooked.  In  diameter  it  differs  little  from  the  blastula  above  described  (fig.  62), 
but  its  depth  is  notably  greater.  Comparing  these  two  stages,  we  conclude  that 
the  deep  subgerminal  region  of  the  earlier  stage  (fig.  62),  which  was  traversed 
by  vacuoles,  has  been  replaced  by  the  deep-lying  mass  of  cells  of  fig.  63.  We 
observe  that  this  thickening  of  the  cellular  mass  has  not  yet  been  accompanied  by 
an  extension  over  the  surrounding  region;  the  mass  is  at  present  compact,  sub- 
spherical,  lying  in  a  smooth  depression  of  the  germinal  wall.  At  one  end  of  the 
cellular  mass  the  segmentation  cavity,  below  the  letters  sc,  represents  all  that 
remains  of  the  intercellular  spaces  of  earlier  stages.  Near  the  opposite  end  is  a 
small  archenteric  cavity,  a,  communicating  with  the  surface  through  the  opening 
bp.  The  archenteron  is  regular  in  outline,  its  marginal  cells  forming  a  somewhat 
epithelial  lining  (fig.  63  B).  It  has  probably  arisen  by  an  invagination  in  pre- 
existing cells,  since  the  cells  lining  its  outer  half  are  slightly  pigmented  and  closely 
resemble  those  of  the  surface  of  the  blastoderm.  Especially  noteworthy  is  this— 
that  behind  the  archenteron,  i.  e. ,  between  it  and  the  germinal  wall,  are  several 
rows  of  cells. 

We  have,  therefore,  evidence  that  in  Chimera  a  gastrula  is  formed  whose 
blastopore  is  located  not  at  the  rim  of  the  early  blastoderm  but  near  it.  It 
is  thus  a  condition  in  which  the  merging  of  the  cells  of  the  blastoderm  with  the 
surrounding  yolk  does  not  yet  take  place  in  that  zone  of  the  blastoderm  in  which  the 
archenteron  is  forming.  We  have  here,  accordingly,  a  condition  which  throws 
light  upon  the  origin  of  the  gastrula  of  sharks,  confirming  in  a  striking  way  the 
interpretations  of  C.  K.  Hoffman  (1896,  Morph.  JB.,  p.  210). 


64  CHIMjEROID   FISHES  AND  THEIR   DEVELOPMENT. 

Continuing  our  examination  of  the  present  specimen,  it  will  be  observed  that 
the  growth  of  the  cell  mass  is  taking  place  at  both  anterior  and  posterior  margins. 
Cells  are  still  being  contributed  to  the  cellular  wall  behind  the  archenteron,  judging 
at  least  from  their  relations  to  the  yolk — such  a  blastomere,  for  example,  as  that 
near  2  having  become  detached  from  the  germinal  wall.  And  at  the  extreme 
anterior  region  of  the  blastoderm  many  cells  are  being  budded  out  of  the  germinal 
wall.  Thus,  as  shown  in  the  detail  (fig.  63  A),  it  will  be  seen  that  in  an  overhanging 
portion  of  the  germinal  wall,  as  below  and  between  the  points  marked  with  aster- 
isks (*),  a  row  of  half  a  dozen  cells  are  clearly  outlined  in  the  wall — a  condition  which 
indicates  strongly  a  similar  origin  for  the  adjacent  cells.  At  lower  points  of  the 


Fig.  63. — Sagittal  section  of  earliest  gastrula.     a,  Archenteric  cavity,     bp,  Blastopore.     sc,  Segmentation  cavity.     I-V  indicate 

position  of  nuclei  in  yolk  region. 
Figs.  63  A  and  B. — Details  of  foregoing  section  at  anteriormost  and  posteriormost  margins  respectively. 

germinal  wall,  finally,  cellular  additions  to  the  blastoderm  are  being  made.  Note- 
worthy in  the  present  section  are  the  vacuoles  which  pass  deeply  into  the  yolk  and 
suggest,  as  we  have  already  noted,  modified  or  suppressed  lines  of  cleavage;  espe- 
cially well  marked  are  those  occurring  in  the  fine  yolk  on  either  side  of  the  blasto- 
derm, since  they  form  a  series  of  vertical  fissures  and  mark  off  masses  of  fine  yolk 
containing  nuclei.  The  vacuoles  also  occur  throughout  the  neighboring  coarse  yolk, 
and  in  connection  with  their  appearance  there  we  note  the  presence  of  merocytes 
which  have  traveled,  as  at  iv,  in,  n  or  i,  far  out  over  the  yolk.  We  note,  lastly, 
the  way  in  which  the  fine  yolk  passes  down  in  rifts  into  the  coarse  yolk,  for  this 
suggests  again  the  modified  holoblastic  condition  of  the  egg. 

The  next  stages  in  gastrulation  deal  with  the  extension  of  the  blastoderm  over 
the  yolk.     Thus  in  fig.  64  is  given 'a  sagittal  section  of  a  stage  in  which  the  diameter 


GASTRULATION. 


of  the  blastoderm  has  doubled  and  during  this  growth  it  has  lost  the  compact  char- 
acter of  the  earlier  stage.  We  recognize,  however,  in  the  cellular  mass  (at  the  left 
in  the  figure,  p-nt)  the  group  of  cells  which  formed  the  ventral  lip  of  the  blastopore, 
and  from  a  detail  of  this  region,  fig.  64*,  we  conclude  that  the  blastopore,  bp,  has 


64" 


Fig.  64. — Sagittal  section  of  gastrula  slightly  older  than  the  preceding.    X  35.     a,  Archenteron ;  bp,  position  of 

former  blastopore ;  ptn.  Cells  of  posterior  lip  of  blastopore ;  .sv,  Segmentation  cavity. 
Fig.  64'. — Detail  of  preceding  section  showing  the  region  of  the  blastopore. 
Fig.  64". — Lateral  section  from  the  series  from  which  fig.  64  was  drawn. 

become  closed,  owing  probably  to  stress  arising  from  the  rapid  extension  backward 
of  the  entire  blastoderm;  and  we  note  in  this  connection  the  greatly  compressed 
character  of  the  cells.  Parenthetically,  we  may  also  call  attention  in  another 


66  CHIM.EROID   FISHES  AND  THEIR  DEVELOPMENT. 

section  (fig.  64  A)  to  the  great  number  of  amitoses  occurring  throughout  the  germinal 
wall,  and  on  the  other  hand,  the  absence  of  mitoses  in  this  region.  Referring  again 
to  fig.  64,  we  interpret  the  cavity  a  as  the  archenteron  of  the  earlier  stage  which 
has  deepened  and  reached  the  germinal  wall,  still  preserving  its  smooth  posterior 
boundary,  but  dilated  anteriorly  and  fading  into  a  mass  of  detached  cells.  And  we 
identify  the  cavity  sc  as  the  segmentation  cavity  now  enlarged  and  with  irregular 
offshoots.  Another  section  of  the  present  specimen  shows,  near  the  side,  fig.  64", 
the  marginal  extent  of  the  dilated  archenteron  and  the  obliteration  in  this  region 
of  the  segmentation  cavity.  Its  major  interest,  however,  is  in  contributing  data 
concerning  the  relation  of  the  blastoderm  to  the  yolk.  Especially  at  the  anterior 
end  we  observe  that  the  cellular  elements,  of  great  size,  have  recently  become 
detached  from  the  yolk. 

The  details  in  the  study  of  this  specimen  deserve  especial  comment,  for  they 
indicate  an  intimate  functional  relationship  between  mitosis  and  amitosis.*  To 
illustrate  these  conditions  a  number  of  details  are  given  in  figs.  64  A-N,  all  drawn 
from  the  foregoing  specimen,  but  from  selected  sections.  We  may  first  refer  to  the 
character  of  the  merocytes.  In  a  detail  of  the  anterior  end  of  this  specimen, 
fig.  64  A,  over  fifty  merocytes  are  present,  most  occurring  in  the  fine  yolk,  but  some 
in  a  superficial  rift  of  coarse  yolk  which  spreads  inward  toward  the  blastoderm.  We 
observe:  numerous  amitoses;  the  masses  of  fine  yolk  whose  distinct  outlines  suggest 
poly  nuclear  blastomeres;  at  one  point  (near  i)a  nucleus  surrounded  with  fine  yolk, 
altogether  suggesting  a  single  blastomere ;  blastomeres  formed  out  of  the  yolk  (2  and 
3);  a  large  clear  blastomere  (4)  which  appears  to  have  budded  out  of  the  germinal 
wall;  and  (5)  a  small  clear  blastomere,  which  has  undoubtedly  been  derived  from 
the  adjacent  yolk.  At  the  opposite  end  of  the  blastoderm  (fig.  64  B),  and  within  it, 
is  a  large  cell  containing  many  nuclei,  some  of  which  are  in  amitotic  division,  and 
similar  appearances  are  observed  further  along  in  the  same  section,  fig.  64  i  and  j. 
In  the  first  of  these,  i,  a  large  blastomere  has  broken  up  into  three  smaller  cells,  in 
the  largest  of  which  the  nucleus  has  subdivided  amitotically  into  at  least  half  a 
dozen  smaller  ones;  in  the  second,  j,  a  blastomere  has  divided  and  in  each  resulting 

*The  merocytes  here  considered  are  regarded  as  products  of  the  segmentation  nuclei.  The  difficulty,  however, 
in  distinguishing  finally  between  the  merocytes  derived  from  the  segmentation  nuclei  or  from  the  sperm-heads  has 
already  been  commented  on  (p.  57). 

Figs.  64  A-N.     Details  of  sections  of  preceding  stage.     (See  page  67.) 
A.     Detail  of  germinal  wall  at  extreme  anterior  end  of  blastoderm.     I  -5,  cells  which  are  arising,  or  have  recently  arisen  from  the  germinal  wall.     There  can  be 

little  question  from  the  yolk-filled  character  of  some  of  these  that  they  have  recently  arisen  from  the  germinal  wall  (i.  e.,  they  can  not  be  cells  which  are 

being  passed  into  the  germinal  wall,  as  His  suggests).     Such  a  cell  as  that  indicated  at  5,  although  destitute  of  yolk  material,  is  so  far  from  the  remaining 

cells  of  the  blastoderm  that  it  could  only  have  been  budded  off  from  the  germinal  wall. 
li.     Detail  of  the  posterior  rim  of  blastoderm  showing  the  origin  of  blastomeres  from  the  yolk  wall.     Observe  that  some  of  the  cells  are  Blled  with  coarse  yolk ; 

others,  3,  have  relatively  little.     The  cell,  2,  just  separated  from  the  germinal  wall,  contains  a  number  of  (amitotic)  nuclei. 
G     Detail  of  wall  of  germinal  yolk.      1 ,  2,  3,  Nuclei  arising  amitotically.  passing  in  the  direction  of  the  floor  of  the  subgerminal  cavity.     4.  Blastomere  arising 

from  the  germinal  wall.     5,  Blastomere  undergoing  amitosis.     6,  Blastomere  arising  from  the  germinal  wall,  and  showing  aster. 

D.  Origin  of  blistomtres  from  the  germinal  wall.     4  and  5,  Blastomeres  recently  separated.      1 ,  2,  and  3,  Nuclei  about  to  be  passed  into  blastomeres. 

E.  Yolk-filled  cell  arising  from  the  germinal  wall,  and  exhibiting  typical  mitosis.     Adjacent  is  a  blastomere  whose  nucleus  is  dividing  amitotically. 
f-    Blastomeres  newly  arisen  from  the  germinal  wall. 

'•'•     Vesicular  nuclei  in  region  near  surface  of  germinal  wall. 

'  /•     Vesicular  nucleus,  undergoing  amitotic  division,  with  adjacent  vacuolar  spaces. 
/ .   I  •   A  .  and  L.     Cells  of  blastoderms  in  some  of  which  amitosis  is  taking  place. 
M  and  A.     Cells  of  blastoderm  dividing  by  atypical  multiple  mitosis. 


MITOSIS  AND  AMITOSIS. 


67 


Of 


N 


Figs.  64   A-N.     Details  of   sections  of   preceding  stage.     (See  bottom  of  opposite  page.) 


68  CHIMvEROID   FISHES   AND  THEIR   DEVELOPMENT. 

blastomere  the  nucleus  has  undergone,  or  is  undergoing,  amitosis.  Now  in  these 
instances  there  can  be  no  question  that  the  amitotic  divisions  are  taking  place  within 
the  blastoderm  itself,  in  a  region  where,  by  analogy,  mitosis  alone  should  occur, 
and  where  later,  indeed,  in  the  same  form,  mitoses  alone  are  found.  And  we  are 
thus  constrained  to  conclude  either  that  amitosis  and  mitosis  are  processes  not  as 
immutably  different  in  fate  as  is  generally  assumed,  or  that  at  a  later  period  the 
amitotic  blastomeres  undergo  disintegration  within  the  blastoderm. 

But  to  continue:  In  fig.  64  c,  from  a  neighboring  section,  we  observe  as  before 
amitosis  occurring  within  the  germinal  wall,  and  this  type  of  nuclear  multiplication 
appears  active  to  an  extraordinary  degree,  as  the  detail,  i,  indicates.  Moreover, 
with  this  activity,  there  is  evidence  from  the  greatly  elongated  character  of  some 
of  the  nuclei,  2,  2,  and  from  the  evident  trails  which  occur,  e.  g.,  at  3,  that  these 
nuclei  are  passing  rapidly  in  the  direction  of  the  surface  of  the  yolk.  We  note  also 
that  cellular  increments,  e.  g.,  in  such  a  cell  as  4,  are  arising  from  the  germinal 
wall,  and,  as  in  the  former  specimen,  amitotic  division  is  present,  5,  in  the  blasto- 
derm proper.  Adjacent  to  this,  and  in  as  close  relation  with  the  germinal  wall, 
there  is  also  evidence  of  mitotic  division,  6.  We  have  seen  that  in  this  section  the 
cell  4  is  arising  out  of  the  germinal  wall ;  if  any  doubt  exists  as  to  possibility  of 
cells  to  arise  from  the  germinal  wall  at  this  late  stage,  we  may  refer  to  the  detail 
shown  from  a  neighboring  section  in  fig.  64  D.  Here  is  present  a  row  of  cells 
arising  in  this  manner:  in  the  wall  itself  occur  the  nuclei  2  and  3,  of  which  the 
latter  is  passing  into  a  lobe-shaped  process  budding  outward  from  the  germinal 
wall.  From  their  position  we  may  safely  conclude  that  4  and  5  have  arisen  in  a 
similar  way.  We  observe,  finally,  that  the  nucleus  in  cell  5  is  undergoing  changes 
in  the  direction  of  amitotic  division. 

Another  interesting  detail  is  given  in  fig.  64  E.  We  have  here  two  cells  which 
appear  to  have  arisen  side  by  side  from  the  germinal  wall;  the  cytoplasm  of  one  is 
clearer,  more  differentiated  apparently  than  its  neighbor,  which  contains  fine  yolk, 
yet  the  nucleus  of  the  cell  lacking  in  yolk  is  undergoing  amitotic  division,  while 
that  of  its  neighbor  is  dividing  mitotically.  In  other  sections  in  this  series  we  note 
the  following  details:  Fig.  64  F,  a  cell  half  budded  from  the  germinal  wall,  also  a 
pair  of  cells  evidently  in  stage  of  telophase,  of  which  the  lower  appears  to  have  just 
budded  out  from  the  germinal  wall;  fig.  640,  two  reticular  nuclei  in  the  germinal 
wall,  products  of  amitotic  division  (cf.  fig.  640),  in  one  of  which  are  two  large 
chromatin  masses;  fig.  64  H,  nucleus  undergoing  a  complicated  series  of  amitotic 
divisions;  this  occurs  near  the  surface  of  the  germinal  wall,  and  we  note  the 
presence  of  vacuoles,  three  in  number,  lying  immediately  above  the  main  masses 
of  the  dividing  nuclei ;  fig.  64  i,  within  the  outline  of  a  single  large  blastomere  occur- 
ring in  the  blastoderm  proper,  three  cells  appear,  and  two  of  these  appear  to 
have  been  derived  from  the  largest,  in  which  we  observe  as  many  as  half  a  dozen 
nuclei;  fig.  64;,  a  cell  in  a  late  stage  of  division  which  shows  three  nuclei  already 


GASTRULATION. 


69 


separate  in  one  of  its  daughter  cells,  and  the  nucleus  in  the  other  about  to  undergo 
amitotic  division;  fig.  64  K,  a  nucleus  similar  to  the  last  occurs  in  a  cell  high  up  in 
the  blastoderm,  and  near  it  a  cell  which  has  undergone  amitosis;  fig.  64  M  and  N, 
two  cells  which  are  undergoing  an  extraordinary  type  of  division;  they  contain 
many  asters,  conspicuous  centrosomes,  but  no  chromosomes;  in  N  the  cell  is  sub- 
dividing into  three  daughter  cells. 

The  significance  of  these  phenomena  is  commented  upon  on  a  later  page,  in 
the  discussion  of  megaspheres  and  yolk  nuclei  in  their  relation  to  germ  layers. 

To  resume  the  question  of  gastrulation : 

The  third  stage  in  the  writer's  material  is  represented  in  surface  view  in  plate  v, 
fig.  31.  It  differs  from  the  earlier  stage  shown  in  this  way,  plate  v,  fig.  30,  in  the 
following  regards:  (i)  The  circumgerminal  ring,  which  had  gradually  been 
extending  and  carrying  its  nuclei  peripherad,  has  faded  out  over  the  surface  of  the 
yolk,  its  proximal  zone  now  alone  noteworthy.  (2)  There  is  a  conspicuous  antero- 
posterior  differentiation.  The  region  of  the  blastopore  is  indicated  by  a  short 
transverse  shadow,  marking  the  cavity  of  the  archenteron,  and  the  segmentation 
cavity  is  denoted  by  a  broad  transverse  area,  the  ends  of  which  as  they  approach 
the  rim  of  the  blastoderm  bend  backward,  giving  a  somewhat  crescentic  shape. 
Three  sections  of  this  blastoderm  are  figured,  the  first,  fig.  65,  is  sagittal,  the 
second,  fig.  65  A,  passes  between  the  points  A- A,  shown  in  the  surface  view,  the 
third,  fig.  65  B,  between  the  points  B-B.  Comparing  the  sagittal  section  fig.  65, 
with  that  of  the  earlier  stage,  fig.  64,  we  observe  increased  growth  at  the  posterior 
rim  of  the  blastoderm;  the  germinal  wall  instead  of  shelving  forward,  now  shelves 
backward,  especially  near  the  surface  of  the  egg,  still  having  below  a  sharp 
shoulder*  against  which  lies  the  remains  of  the  posterior  lip  of  the  blastopore,  pm< 
of  earlier  stages, — this  region,  in  short,  is  being  overgrown  by  the  blastoderm  as  it 
progresses  hindward.  The  archenteron  thus  remains,  as  at  a,  separated  only 
imperfectly  from  the  segmentation  cavity,  sc,  which  is  now  of  great  size.  This 
condition,  indeed,  is  well  shown  in  the  more  lateral  sections,  figs.  65  A  and  B,  and 
they  indicate  as  well  the  narrow  limits  of  the  archenteron;  the  sides  of  which,  it 
will  here  be  seen,  are  practically  confluent  with  the  sides  of  the  segmentation  cavity. 
As  in  the  preceding  stage,  noteworthy  relations  exist  between  the  blastoderm  and 
the  yolk.  We  observe,  for  example,  that  in  the  more  lateral  section  a  tongue  of 
coarse  yolk  passes  inward  close  to  the  surface  of  the  germinal  wall,  and  we  obtain 
evidence  that  the  row  of  neighboring  cells  has  been  formed  by  actual  outbudding. 
In  these  cells  amitosis  occurs,  as  in  the  previous  stage.  These  cells,  it  may  be 
remarked,  do  not  long  remain  in  their  subjacent  position,  for,  identified  by  the 
coarse  yolk  they  contain,  they  can  be  traced  into  the  blastoderm  and  are  found 
widely  scattered  among  other  cells. 


*  I'is-ti-i'fs  is  a  second  shoulder  which  corresponds  to  the  anterior  germinal  wall  of  the  stage  shown  in  fig.  63.     In 
both  regions,  then,  the  blastoderm  has  overgrown  the  surface  of  the  egg. 


70  CHIlvLEROID   FISHES  AND  THEIR   DEVELOPMENT. 

The  fourth  stage  in  gastrulation  appears  in  surface  view  in  plate  v,  fig.  32,  and 
is  but  two  days  older  than  the  preceding,  plate  v,  fig.  31.  It  shows  the  following 
advances:  (i)  The  embryo  proper  makes  its  appearance  in  a  small  depression,  and 
is  conspicuous  on  account  of  the  dark  adjacent  shadows;  (2)  the  center  of  the 
blastoderm  rises  as  a  circular  plateau,  leaving  at  its  base  a  well-marked  flattened 
rim;  surrounding  this  the  circumgerminal  ring  has  largely  faded  away,  its  nuclei 


Fig.  65. — Sagittal  section  of  gastrula  slightly  older  than  the  preceding, 
a,  Archenteron.        sc,  Segmentation  cavity. 
put,  Posterior  mass  of  cells  (in  region  of  ventral  lip  of  blastopore). 

Fig.  65  A. — Section  parallel  to  preceding,  but  situated  further  at  the  side. 
Fig.  65  B. — Section  parallel  to  preceding,  but  more  nearly  marginal. 
Fig.  65  C. — Detail  showing  coarse  yolk. 

now  having  passed  far  out  over  and  into  the  yolk;*  (3)  anteriorly  the  segmentation 
cavity  is  becoming  restricted  to  a  small  area,  appearing  in  surface  view  as  a  light- 
colored  tract  near  the  rim  of  the  blastoderm.  Two  sections  of  this  blastoderm  are 
figured,  one  sagittal  (fig.  66),  the  other  (fig.  66  A)  passing  between  the  points  A- A 
shown  in  surface  view.  Contrasting  the  sagittal  section  (fig.  66)  with  that  of  the 

*  The  figure  represents  the  circumgerminal  zone  as  too  wide  and  conspicuous,  an  inaccuracy  which  was  noticed 
too  late  for  correction. 


GASTRULATION.  7 1 

earlier  stage  (fig.  65),  we  notice  that  (a)  almost  the  entire  flattened  rim  of  the 
blastoderm  has  been  added ;  that  (b)  in  the  posterior  portion  of  this  rim  the  ectoderm 
is  already  differentiating  the  medullary  plate  of  the  embryo,  m ;  that  (c)  the  major 
growth  has  taken  place  backward — in  witness  of  this,  contrast  the  distance  between 
the  anterior  end  of  the  archenteron  and  the  posterior  rim  of  the  blastopore  in  these 
two  stages;  that  (cT)  in  this  connection  the  main  cell-mass  extends  itself  dorsalward 
and  becomes  the  plateau-like  region  of  the  blastoderm ;  that  (<?)  the  germinal  wall 
rising  abruptly  beside  the  archenteron  in  the  ear-tier  stage  becomes  excavated  in 


bf 


Fig.  66. — Sagittal  section  of  gastrula  in  which  ihe  embryo  is  appearing. 


«i  Archenleron. 

'>  Region  of  outermost  margin  of  ventral  lip  of  blastopore. 

jnn,  Posterior  mass  of  cells  (in  position  of  ventral  lip  of  blastopore). 


/(/'t  Region  of  blastopore. 

"'.  Thickening  in  medullary  plate  of  embryo. 

*'',  Segmentation  cavity. 


Fig.  66   A. — Section  (lateral)  parallel  to  the  preceding. 

the  later,  a  portion  of  its  material,  at  least,  being  represented  by  the  spongy  mass 
of  cells  which  now  forms  the  floor  of  the  archenteron,  a;  that  finally  (/)  there  is 
evidence  that  the  posterior  rim  of  the  blastoderm  is  rolling  inward,  the  surface  of 
the  blastoderm  growing  more  rapidly  in  this  region  than  the  lower  layer  with  which 
it  is  connected.  Detailed  examination  of  the  sections,  however,  leads  us  to  the 
belief  that  the  process  of  inrolling  extends  only  as  far  as  the  point  i  (fig.  66) ;  just 
above  this  the  inrolled  rim  of  the  blastoderm  merges  with  the  cells  arising  from 
the  germinal  wall,  and  from  this  point  inward  openings  occur  between  the  cells 
and  communicate  with  the  archenteron.  The  section  (fig.  66  A)  already  referred 


72  CHIM^EROID   FISHES   AND   THEIR   DEVELOPMENT. 

to  as  passing  slightly  to  one  side  of  the  sagittal  plane  shows  favorably  the 
thickening  of  the  ectoderm  at  the  side  of  the  medullary  plate  and  its  inbending. 
We  here  observe  also  the  reduced  size  of  the  segmentation  cavity,  the  thickening 
of  the  cell  mass  roofing  the  archenteron,  and  the  thinning  out  of  the  mass  of  cells, 
pm,  forming  its  floor. 

We  may  at  this  point  consider  conveniently  the  general  bearing  of  the  process  of 
early  gastrulation  in  the  Chimseroid.  We  have  seen  that: 

(a)  In  an  early  stage  an  archenteron  was  present  (fig.  63),  whose  ventral  wall 
was  composed  of  cells  and  whose  axis  was  at  right  angles  to  the  surface  of  the 
blastoderm. 

(<$)  In  a  second  stage,  the  area  of  the  blastoderm  had  increased,  and  the  blasto- 
pore  was  closed  (fig.  64);  its  position  (fig.  64  A),  however,  accurately  located,  but 
more  posterior  than  in  the  first  stage;  also  the  archenteron  has  greatly  increased 
in  size. 

(c)  At  a  third  stage  (fig.  65),  the  location  of  the  blastopore  can  not  be 
accurately  determined,  although  it  is  certainly  near  the  hindmost  point  of  the 
blastoderm ;  the  archenteron  is  less  definite,  and  its  long  axis,  which  remains  parallel 
to  the  neighboring  germinal  wall,  becomes  tilted  backward,  as  indicated  by  the 
arrow  in  the  figure:  and  the  cells,  pm,  which  correspond  to  the  ventral  (posterior) 
wall  of  the  archenteron,  now  occupy  a  position  further  under  and  further  forward 
than  in  earlier  stages,  in  consequence  of  the  hindward  extension  of  the  blastoderm. 

(cf)  Finally  (fig.  66),  this  hindward  extension  is  so  expressed  that  the  position 
of  the  early  blastopore  shifts  under  the  rim  of  the  blastoderm  and  comes  to  appear 
at  the  point  bp;  concomitantly  the  archenteron  increases  in  size,  its  axis  lying 
nearly  parallel  to  the  surface  and  its  ventral  wall  developing  extensively  both  in 
thickness  and  in  (anterior)  extension.  From  these  conditions  it  follows  that  in  the 
later  gastrulation  of  Chimsera  we  are  dealing  with  a  reopening  of  the  blastopore  of 
an  earlier  stage.  Accordingly,  in  contrast  with  gastrulation  in  sharks,  Chimaera 
preserves  the  primitive  blastopore  within  the  blastoderm  itself.  This  stage, 
however,  is  an  evanescent  one.  In  connection  probably  with  a  change  in  nutritive 
values,  whereby  the  yolk  is  passed  to  the  archenteron  from  a  source  more  and 
more  postero-ventral  there  is  a  constant  tendency  for  the  cells  of  the  archenteron 
to  be  drawn,  both  in  ontogeny  and  in  phylogeny,  closer  to  the  source  of  nutriment. 
For  this  reason  the  cells  of  the  archenteron  multiply  more  rapidly  from  below  than 
from  above  (/'.  e. ,  the  region  where  primitively  they  were  invaginated  from  the 
ectoderm)  with  a  result  that  the  blastopore  becomes  of  less  and  less  importance  in 
early  stages.  It  is  suggested,  also,  that  during  this  growth  there  is  a  constant 
convection  of  the  cells  of  the  blastoderm,  in  the  process  of  which  elements  formed 
in  the  region  of  the  posterior  wall  of  the  archenteron  pass  downward  and  forward. 
Part  passu,  the  posterior  rim  of  the  blastoderm,  including  the  region  of  the  blasto- 
pore, extends  first  backward,  then  downward  and  inward;  it  thus  comes  finally  to 
lie  under  the  rim  (i.  e.,  the  later  rim)  of  the  blastoderm. 


GASTRULA    OF    SHARK    AND    CHIMERA. 


73 


We  have  emphasized  these  conditions  of  growth  in  Chimsera,  since  they  serve, 
I  conclude,  to  explain  the  gastrulation  of  the  shark,  a  process  so  puzzling  that 
Samassa  (1895)  has  even  gone  so  far  as  to  deny  its  presence,  sensu  stricto,  in  this 
group.  According  to  the  present  interpretation  the  primitive  shark  had,  like  Chi- 
maera,  a  blastopore  which  opened  near  but  not  at  the  rim  of  the  blastoderm;  in 
this  position  it  next  became  a  rudimentary  organ,  since,  apparently,  the  conditions 
governing  the  increase  of  cells  in  the  archenteron  suffered  a  change — inasmuch  as 
they  came  to  receive  their  nutriment  directly  front  the  neighboring  germinal  wall 
instead  of  indirectly,  i.  e.,  through  a  process  of  continued  invagination  at  the 
blastopore.  Accordingly,  in  the  development  of  modern  sharks  the  blastopore 


Fig.  67.     Diagrams  comparing  gastrulae  of  Chimaera  and  Selachian.     A  and  B,  Earlier  and  later  stages  in  gastrula  of  Chimeera 
colliei.     C  and  1~>,  Earlier  and  later  gastrulae  of  shark  (mainly  after  Riickert). 

O,  Archenteron.     dl,  Dorsal  lip  of  blastopore.     sc,  Segmentation  cavity,     vl.  Ventral  lip  of  blastopore. 

fails  to  appear  within  the  blastodermal  disc,  since  here  it  has  long  been  functionless. 
But  obviously  the  blastopore  would  again  become  important  in  the  economy  of 
gastrulation,  if  nutritive  material  were  brought  into  its  neighborhood  by  any  process 
in  the  growth  of  the  blastoderm  or  in  the  encroachment  of  the  germinal  wall. 
Thus  we  may  infer  that  it  would  again  become  a  functional  organ  when  its  position 
was  transferred  to  the  rim  of  the  blastoderm.  In  this  position  it  still  occurs 
exceptionally,  as  C.  K.  Hoffman  has  shown  in  Acanthias,  *  or  it  may  indeed  reopen 
deeper  under  the  rim  of  the  blastoderm,  as  the  majority  of  investigators  maintain. 


*In  a  letter,  which  I  am  permitted  to  quote  (July,  1903),  from  Professor  Hoffman,  the  comparison  is  accepted  as 
follows:  "In  Chimaera  the  blastopore  is  located  near  and  in  Acanthias  at  the  rim  of  the  early  blastoderm.  For  the 
rest  the  archenteron  and  the  open  blastopore  of  Acanthias  agree  entirely  with  those  of  Chimgera.  Acanthias  forms 
the  bridge  (in  this  regard)  between  Chimaera  and  other  sharks  and  furnishes  us  the  key  to  the  problem  of  gastrulation 
of  the  other  sharks." 


74 


CHIMyEROID  FISHES  AND  THEIR   DEVELOPMENT. 


To  make  the  comparison  of  the  gastrulae  of  Chimaera  and  Shark  more  concrete 
we  have  figured  two  stages  side  by  side  (fig.  67,  A  and  c,  B  and  D).  We  need 
only  add  to  the  foregoing  text  the  remark  that  the  archenteron  and  segmentation 
cavity  are  more  distinct  in  Chimaera,  and  that  the  differentiation  of  the  embryo 
takes  place  in  a  more  restricted  area.  We  append  also  (fig.  68,  A,  B,  c)  a  scheme 
expressing  our  interpretation  of  the  mode  of  origin  of  the  meroblastic  gastrula  in 
this  form.  In  A  is  pictured  a  sagittal  section  of  an  early  gastrula  of  a  holoblastic 
type,  and  between  the  points  marked  with  asterisks  is  indicated  the  narrow  zone 
below  which  the  amount  of  yolk  is  supposed  to  have  notably  increased.  In  B,  the 
second  stage  in  this  evolution,  is  a  condition  not  unlike  the  late  gastrula  in  Chimaera: 
The  yolk  mass  still  segments,  and  the  ventral  lip,  vl,  passes  inward  and  forward  as 
the  dorsal  lip  rolls  backward  and  inward.  In  c,  finally,  is  attained  the  condition  in 
sharks:  Archenteron  and  segmentation  cavity  merge;  segmentation  is  lost  in  the 


Fig.  68. — -Diagrams  suggesting  origin  of  meroblaslic  character  of  egg  of  shaik. 

A.  Sagittal  section  of  early  gastrula  of  holoblastic  egg  (e.  g.,  Petromyzon).  />.  Section  showing  conditions  similar 
to  those  in  Chimaera  colliei  (cf.  fig.  66).  C.  Section  of  gastrula  of  shark,  arch,  Archenteron;  v!,  ventral 
lip  of  blastopore  ;  sc,  segmentation  cavity. 

yolk  mass,  and  the  latter  comes  to  pass  its  nutriment  into  the  blastoderm  indirectly, 
i.  e.,  as  nourishment  for  the  growth  and  multiplication  of  the  cells  already  formed, 
instead  of  directly,  i.  e.,  in  the  form  of  new  yolk-filled  blastomeres,  and  from  this 
process  there  results  a  smooth  germinal  wall.  This  interpretation  agrees  in  general 
with  that  lately  restated  by  Ziegler  (Lehrbuch  Entwicklungsgeschichte,  1901,  pp. 
352-353);  it  differs  in  the  interpretation  of  the  fate  of  the  ventral  lip  of  the 
blastopore.  According  to  the  older  view  the  ventral  lip  remains  more  or  less 
passive,  in  the  present  interpretation  it  has  undergone  a  marked  change;  the  cells 
which  primitively  formed  the  ventral  lip  of  the  blastopore  are  to  be  sought  in  the 
region  vl,  on  the  floor  of  the  archenteron.  The  de  facto  ventral  lip  of  the 
blastopore  (i.  e. ,  in  all  stages  but  the  earliest)  is  accordingly  a  secondary  structure, 
which  arises  from  the  new  conditions  attending  the  overgrowth  of  the  blastoderm. 


LATER  G  A  STROLL.  75 

LATER   GASTRUL^E. 

Surface  views  of  three  later  gastrulse  are  pictured  in  plate  v,  figs.  33-35,  a 
series  in  which  the  body  of  the  embryo  becomes  distinctly  differentiated.  In  the 
first  it  occurs  as  a  lip-like  thickening,  the  blastoderm  itself  having  become  some- 
what larger  in  diameter  and  flatter  than  in  the  previous  stage.  In  the  present 
specimen,  which  was  examined  after  my  interest  was  aroused  in  the  matter  of  the 
peripherad  migration  of  the  yolk-nuclei,  these  structures  could  be  seen*  spread  out 
widely  over  the  neighboring  surface  of  the  yolk.  Tlfe  second  stage,  plate  v,  fig.  34, 
resembles  outwardly  a  shark  embryo  at  Balfour's  stage  B;  the  light  area  in  the 
anterior  and  median  portion  of  the  blastoderm,  which  marks  the  cleavage  cavity,  is, 
however,  larger  than  in  any  selachian  hitherto  described.  In  the  third  stage,  plate  v, 
fig.  35,  the  embryo  arises  as  a  knob-like  eminence,  its  tail  end  projecting  some- 
what over  the  edge  of  the  blastoderm;  anteriorly  the  surface  of  the  blastoderm 
becomes  thin  and  transparent,  and  it  here  assumes  a  peculiar  vesicular  character. 

DETAILS  OF  THE  LATER  GASTRULA  OF  PLATE  V,  FIG.  35. 

This  stage,  although  scarcely  later  than  Balfour's  stage  B  in  shark  nomencla- 
ture, is  remarkable  for  the  concentration  of  its  elements.  Thus,  if  we  compare  it 
in  point  of  size  with  a  similar  stage  in  Pristiurus,  measuring  it  always  in  terms  of  its 
blastoderm,  it  is  of  much  smaller  size.  At  this  stage  the  length  of  an  embryo  of 
Torpedo  measures  about  one-third  the  diameter  of  its  blastoderm,  that  of  Pristiurus 
about  one-eighth,  and  that  of  Chimsera  not  more  than  one-twelfth.  Moreover, 
its  component  parts  are  already  more  highly  differentiated. 

A  number  of  details  of  this  stage  are  given  in  plate  vi,  fig.  39,  and  figs.  39  A-E. 
In  the  first  of  these  (fig.  39)  the  embryo  with  its  adjacent  blastoderm  is  viewed  as 
an  opaque  object;  it  appears  next  in  similar  position  (A)  but  as  a  transparent  object, 
showing  ectoderm,  entoderm,  and  archenteron.  Behind  the  embryo  the  surface  of 
the  yolk  shows  a  series  of  lines  representing  either  surface  fissures  or  vacuoles, 
related,  as  we  have  concluded,  to  lines  of  cleavage.  In  the  following  figures  the 
embryo  is  viewed  from  an  antero-dorsal  direction  (B),  postero-dorsal  (c),  postero- 
median  (D),  and  postero-ventral  (E).  The  mesoblast  is  well  indicated  in  plate  vi, 
fig-  39  n>  also  the  extent  of  the  thickening  of  the  ectoblast  forming  the  posterior 
margin  of  the  embryonic  body.  In  connection  with  these  figures  we  may  refer  to 
the  series,  fig.  69  A-M,  drawn  from  sections  of  this  embryo  cut  parallel  to  the 
neighboring  rim  of  the  blastoderm  (i.  e.,  transverse,  although  slightly  oblique  to 
the  axis  of  the  embryo),  and  point  out  the  following  features:  (i)  The  size  and 
definiteness  of  the  gut,  an  important  factor  in  establishing  the  contour  of  the 
embryonic  body;  the  gut  acquires  the  cavity,  gc  (which  communicates  with  the 
yolk  region  only  for  a  short  space  near  the  rim  of  the  blastoderm,  c,  and  accumu- 
lates around  its  anterior  end  the  bulk  of  the  mesoblast,  mes).  (2)  The  fusion  of 
ecto-  and  entoblast  occurring  not  merely  at  the  tail  end  of  the  embryonic  body  but 

*The  circumgerminal  zone  is,  however,  shown  too  distinctly  in  the  present  figure;  its  color  should  resemble  rather 
that  in  plate  v,  fig.  34. 


76  CHIMyEROID   FISHES  AND  THEIR   DEVELOPMENT. 

far  forward,  almost  to  the  end  of  the  embryonic  gut,  the  band  of  fusion  extending 
in  a  narrow  zone  as  denoted  at  x,  fig.  69  n.  (3)  The  concentration  of  the  yolk- 
entoblast  under  the  embryonic  body;  this  becomes  conspicuous  quite  in  front  of  the 
embryonic  gut,  then  merges  with  the  gut,  then  separates  from  it,  and,  as  the  lumen 
of  the  gut  opens  out  ventrally,  it  proceeds  backward  in  a  layer  finally  rounding 


H 


D 


F 


Fig.   69  A-M. — Transverse  sections  through  early  embryo  and   neighboring  blastoderm  of  stage  corresponding  to  that  of  plate  V, 

fig.  35.     The  series  passes  from  in  front  backward. 

C,  Yolk  region  intruding  between  caudal  folds ;  <!<*,  gut  cavity;   '",  mesoblast;  :V,  yolk  lying  in  cavity  of  gut ; 
X,  fold  near  posterior  end  of  embryo  where  ectoderm  and  entoderm  merge. 

outward  on  either  side.  (4)  The  presence  in  the  cavity  of  the  embryonic  gut  of 
small  masses  of  the  disintegrating  segments  of  the  egg  (fig.  69  G,  gc),  which  serve 
probably  as  food,  interesting  in  connection  with  the  fate  of  the  yolk  in  Chimsera 
(cf.  in  stages  of  Plate  vm).  Contrasting  the  foregoing  conditions  with  those  in  an 
elasmobranch  in  stage  B  (e.  g.,  as  shown  by  the  Zieglers,  Archiv  f.  mikr.  Anatomic, 


PRECOCIOUS   DEVELOPMENT   IN   EARLY   EMBRYO. 


77 


6 


N. 


Bd.  xxxix,  Taf.  in),  we  note  that  the  Chimse- 
roid  although  smaller  is  much  less  flattened 
out;  that  the  gut  which  is  flattened  against  the 
yolk  in  the  elasmobranch  is  in  Chimaera  defi- 
nitely formed  and  provided  with  a  distinct 
lumen;  that  the  lateral  contour  of  the  embryo's 
body  in  Chimsera  is  already  developed,  the 
ectoderm  in  the  Jiinder  region  fusing  with  the 
entoderm;  that  the  yolk  entoblast  thickens  in 
the  median  axial  line,  a  feature  lacking  in  the 
shark,  but  important  doubtless  in  the  early 
assimilation  of  the  yolk. 

From  the  foregoing  details  one  is  led  to 
conclude  that  in  Chimsera  ' '  precocious  segre- 
gation" has  been  developed  to  a  noteworthy 
degree.      In    spite   of   the    small    size    of   the 
embryo,   both  relatively  and  actually,   it  has 
already  made  strides  in  the  direction 
of  attaining  its  definite  form,  outstrip- 
ping  in    these    regards    the  elasmo- 
branch ;  thus  it  has  already  developed 
gut   outline,  definitely  arranged   the 
mesoblast,   separated  practically  the 
sides  of  the  embryo  from  the  blasto- 
derm, and  has  specially  concentrated 
the  yolk  entoblast  in  the  axial  region. 
Accordingly,    in  these  regards,   Chi- 
msera stands  separate  from  the  elas- 
mobranchs;  transitional,  however,  is 
Callorhynchus,  judging  from   figures 
recently  given  by  Schauinsland  (c.  g. , 
in  his  plate  xn). 

An  idea  of  the  complicated 
nature  of  the  blastoderm  at  this  stage 
(plate  v,  fig.  35),  both  in  itself  and  in 
its  relation  to  the  yolk,  may  be  had  by 
examination  of  fig.  70.  This  repre- 
sents part  of  a  section  which  passes 
through  the  blastoderm  transversely, 
somewhat  in  front  of  the  embryo. 

Fig.  70. — Detail  ol  section  of  preceding  embryo.  The  section  is  transverse  and  passes  near 
middle  of  blastoderm.  It  shows  particularly  the  early  differentiation  of  the  vacuolar  area. 
,ili.  Peripheral  zone  of  blaslod  erro  ;  b-c,  central  region  of  blastoderm  ;  1-5,  centers  of  proliferation  of  ecto- 
derm into  mesoderm  ;  6-7,  Lower  ends  of  these  proliferations  in  their  relation  to  entoderm  ;  8,  amitosis  in 
spongy  trabeculae ;  9,  grouping  of  mesoderra  cells  to  form  vessels;  10-1  I,  centers,  large  and  small,  of 
germinal-yolk  in  which  or  near  which  nuclear  elements  are  dividing  amilotically. 


/.  .   •" 


-g  CH1MJEROID   FISHES  AND  THEIR   DEVELOPMENT. 

We  notice,  first  of  all,  that  the  peripheral  zone  of  the  blastoderm  (between  the 
points  a-fr)  is  less  complicated  than  its  central  portion  (between  b-c).  The  periph- 
eral zone  is,  however,  more  highly  differentiated  than  in  a  similar  region  in  an 
elasmobranch  (cf.  Riickert's  memoir  in  Kupffer's  Festschrift,  plate  vn,  fig.  75); 
witness  the  definite  character  of  the  ectoblast  and  yolk  entoblast,  and  the  gigantic 
size  of  many  of  the  mesoblast  cells.  But  it  is  in  the  central  region  of  the  blasto- 
derm where  the  conditions  are  most  extraordinary;  we  observe,  that  at  many 
points,  1-5,  masses  of  cells  extend  downward  from  the  ectoderm,  proliferating  in 
ridges,  sometimes  giving  rise  to  root-like  processes.  These  terminate  below  either 
freely,  or  they  may  actually  fuse  with  the  entoblast;  at  various  points,  6,  they  lie 
close  to  the  entoblast ;  at  7  is  shown  a  point  where  they  become  continuous  with  the 
entoblast  (the  continuity  to  be  traced  in  the  serial  sections).  They  thus  form  the 
spongy  meshwork  which  we  have  already  noted  in  the  surface  view  of  this  stage, 
a  condition  of  complication,  which,  as  far  as  I  am  aware,  is  unknown  in  the 
extra-embryonal  blastoderm  of  so  early  a  stage  in  any  other  vertebrate. 

We  note  in  connection  with  the  spongy  character  of  the  blastoderm  the 
presence  of  many  large  cells  (unshaded  in  the  figure),  some  of  which,  like  many  in 
the  neighboring  spongy  trabecute,  are  undergoing  numerous  divisions  (amitotic)  as 
at  8.*  To  understand  the  meaning  of  this  spongy  blastoderm  one  should  first 
consider  it  in  its  prospective  value.  Later  specimens  show  that  in  this  region 
appear  blood-vessels,  and  in  the  present  early  preparation — and  even  indeed  in 
earlier  ones,  we  are  evidently  dealing  with  the  beginnings  of  vascular  structures. 
In  fact  in  the  trabeculs  themselves  we  find  at  various  points  (9)  the  cells  already 
grouped  together  so  as  to  form  cavities,  and  in  the  latter  large  granular  cells  are 
undergoing  subdivision,  in  the  direction  evidently  of  blood-building.  In  this  character 
again,  it  will  be  remarked  there  is  given  an  important  instance  of  the  precocious 
mode  of  development  of  Chimera.  In  other  words,  in  this  form  at  a  period  which 
outwardly  suggests  stage  B  of  the  shark  the  vascular  development  in  the  extra- 
embryonal  blastoderm  is  (approximately)  equivalent  to  the  shark's  in  stage  E. 

*We  have  here  again  evidence  against  the  commonly  accepted  view  (of  Flemming,  Ziegler,  and  von  Rath)  as  to 
the  significance  of  amitosis.  Admitting  that  these  cells  come  to  form  blood  and  blood-vessels,  it  must  also  be  granted, 
as  the  following  evidence  shows,  that  the  blastoderm  becomes  part  of  the  young  fish,  and  therefore  the  behavior  of  its 
cellular  components  is  not  to  be  compared  with  that  of  the  vitellophagous  periblast  nuclei  in  the  teleost.  Of  course 
it  will  be  seen,  on  the  other  hand,  that  the  adherent  of  the  Flemmingian  view  might  object  that  although  the  blastoderm 
itself  was  a  permanent  structure  of  the  embryo  it  might  none  the  less  contain  provisional  cellular  elements  (nutritive) . 
He  will  admit,  however,  that  this  rarified  view  as  to  the  fate  of  component  elements  of  the  blastoderm  receives  little 
support  from  the  examination  of  related  elasmobranchian  structures. 

The  present  evidence,  it  seems  to  me,  favors  the  view  that  amitosis  is  but  a  symptom  of  early  and  rapid  cell- 
multiplication.  Such  a  need  for  rapid  division  often  occurs  in  evanescent  structures,  and  hence  it  may  happen  that 
this  type  of  division  has  been  given  less  consideration  than  it  is  justly  entitled  to,  from  the  standpoints  both  of  cell 
physiology  and  cell  philosophy.  In  this  matter  I  need  merely  mention,  in  view  of  the  scope  of  the  present  paper,  that 
there  is  rapidly  accumulating  a  mass  of  evidence  against  the  decadent  character  of  amitosis.  In  the  nature  of  such 
evidence  are  the  observations  of  Conklin  (Am.  Nat.,  Oct.,  1903)  on  the  egg  follicle  cells  of  Gryllus  ;  Kellogg 's  results  on 
similar  structures  in  Hydrophilus  (Science,  Mar.  4,  1904);  also  H.  L.  Osborn's  observations  on  Fasciolaria  (Science, 
Feb.  5,  1904)  in  which  amitosis  occurs  in  stages  of  gastrulation  ;  Boeke's  statements  that  in  teleosts  mitotic  may 
arise  from  amitotic  nuclei  (Petrus  Camper,  vol.  n,  Afl.  2,  pp.  161,  1902);  finally,  Child's  "Amitosis  in  Moniezia"  (Anat. 
Anz.,  vol.  xxv,  1904). 


EXTRA-EMBRYONIC  BLASTODERM. 


79 


The  complexity  of  the  foregoing  conditions  (fig.  70)  applies  as 
well  to  the  yolk  region  as  to  the  blastoderm  itself.  Without  enter- 
ing into  undue  detail  we  may  note  the  following:  Extreme  vacuo- 
lization  of  the  subgerminal  region  (the  vacuoles  at  the  right  in 
the  figure  are  indicated  by  dotted  lines);  they  usually  occur 

in  or  in  association  with  the  lighter  areas 
of  the  germinal  yolk.  If  we  regard  the 
vacuoles  in  the  earlier  stage  as  retaining 
the  character  of  intercellular  spaces,  they 
have  by  this  time  undergone,  in  part  at 
least,  change  of  function,  serving  now  as 
nutriment  purveyors  to  the  yolk  ento- 
blast.  In  this  connection  we  find  that  at 
various  points,  10,  the  coarse  yolk  is 
traversed  by  fine  yolk  in  rifts,  whose 
shape  suggests  that  of  the  vacuoles  of 
earlier  stages.  In  this  fine  yolk,  more- 
over, many  nuclei  are  present,  and,  judg- 
ing from  numerous  amitoses,  dividing 
rapidly.  In  addition  to  these  rifts  of  fine 
yolk,  we  note  that  there  occur  at  many 
places  throughout  the  coarse  yolk  small 
areas  of  fine  yolk,  1 1 ;  these  have  in  nearly 
every  case  nuclei  in  or  near  them,  and 
we  have  thus  ground  for  regarding  the 
yolk  region  of  the  egg  not  as  a  syncytium 
pur,  but  rather  as  a  mass  of  yolk-filled 
cells  whose  boundaries  have  broken  down, 
but  whose  individuality  as  cells  has  not 
yet  been  wholly  lost. 

A  second  section  of  the  extra-embry- 
onic blastoderm  of  this  stage  is  shown  in 
fig.  70  A,  a  detail  of  a  section  passing 
through  the  blastoderm  considerably  in 
front  of  the  preceding  section.  Here  is  indicated  even  better 
than  before  the  presence  of  giant  cells  which  have  arisen  from 
the  yolk,  migrated  outward,  and  are  undergoing  division  in  the 
region  immediately  below  the  ectoderm.  At  one  point  (a)  a 
yolk  cell  of  gigantic  size  is  shown  (unshaded);  at  other  points 
(b,  b,  b}  similar  yolk  cells  are  undergoing  division  by  amitosis. 

Figs.  70  A  and  B.  -Sections  of  stage  of  early  embryo  figured  in  fig.  69. 

A.  Portion  of  extra-embryonic  region  in  section  corresponding  to  fig.  69  B. 

B.  Embryonic  and  extra-embryonic  regions  in  section  similar  to  fig.  69  C. 


80  CHIM^ROID   FISHES  AND  THEIR   DEVELOPMENT. 

Into  this  region  extends  a  delicate  layer  of  mesoblast  (W);  and  here  and  there 
groupings  of  cells  of  this  layer,  as  at  v,  suggest  the  formation  of  blood  vessels. 
Under  the  gigantic  cell,  one  notes  that  the  cells  of  the  mesoblast  layer  are  of 
remarkable  size. 

Another  section,  given  in  fig.  70  B,  pictures  details  of  a  section  similar  to  fig. 
69  G.  This  illustrates  particularly  a  subgerminal  zone  containing  large  yolk  nuclei ; 
of  these  some  are  situated  close  to  the  surface  of  the  subgerminal  wall,  and  one  (W) 
has  passed  into  the  entoderm.  This  obviously  cannot  be  confused  with  the  adja- 
cent entoderm  cells,  if  only  on  account  of  its  greater  size.  In  this  section  a  special 
area  of  formative  yolk  is  shown  underlying  the  periphery  of  the  blastoderm.  Under 
the  embryo  itself  the  formative  yolk  attains  the  surface  notably  at  the  sides  of  the 
embryonic  body,  and  it  is  from  this  region  that  the  cells  appear  to  be  passed  into 
the  embryo.  Less  activity  is  probably  present  in  the  ventral  median  line,  on 
account  of  the  quantity  of  coarse  yolk  which  is  here  present. 

LATER  GASTRULA.     EMBRYO  WITH  OPEN  MEDULLARY  FOLDS. 

This  stage,  figured  in  surface  view,  plate  v,  fig.  36,  and  in  detail,  plate  vi,  fig.  40, 
may  be  compared  with  Balfour's  stage  D  in  elasmobranch.  In  spite  of  the  conspicu- 
ous growth  of  the  embryo,  the  blastoderm,  it  may  be  noted,  remains  remarkably 
small  in  size.  In  this  stage  the  blastoderm  of  Chimaera  shows  a  well-marked 
central  area,  which  on  closer  examination  is  found  to  be  made  up  of  spongy  mesh- 
work  ;  there  is  also  a  somewhat  thickened  rim,  and  a  marginal  zone,  the  latter 
shown  in  sections  to  be  formed  of  peristomial  mesoblast.  Beyond  the  limits  of  the 
blastoderm  the  surface  of  the  yolk  showed  faintly  diverging  lines  which  suggested 
cleavage  planes.  (Cf.  plate  vi,  fig.  39  A.)  The  embryo  itself,  when  viewed  as  a 
transparent  object,  plate  vi,  fig.  40,  shows  shark-like  medullary  folds,  more  delicate, 
however,  and  narrower  in  proportions.  The  tail  folds  are  less  conspicuous  ;  the 
mesoblast  concentrating  in  this  region  shows  on  each  side  a  dark  area,  the  rela- 
tions of  which  are  referred  to  later. 

DETAILS  OF  STAGE  D. 

Transverse  sections  of  the  embryo  and  the  neighboring  blastoderm  in  this 
stage  are  pictured  in  fig.  71,  A-i.  Thus  beginning  with  a  section  through  the  tail 
folds,  we  see  in  B,  ectoderm  and  entoderm  continuous  in  the  chordal  region.  In 
this  section  the  mesoderm  merges  with  the  entoderm  not  at  the  sides  of  the  chordal 
region,  but  near  the  margin  of  the  blastoderm,  thus  suggesting  the  theoretical  condi- 
tion in  the  origin  of  the  mesoblast  advocated  by  Graham  Kerr.  In  section  c  (at  the 
left  side,  the  plane  being  slightly  oblique)  the  side  of  the  blastoderm  is  coming  into 
functional  connection  with  the  yolk;  the  notochord  is  here  being  folded  off  from 
the  entoderm ;  the  latter  is  now  a  thick,  flattened  layer,  its  outer  half  lying  apposed 
to  the  yolk  wall.  In  D  the  section  shows  the  beginning  of  the  neural  folds  ;  below 
them  is  a  well  formed  layer  of  mesoblast,  also  the  dorsal  wall  of  the  gut;  the  gut 
lumen  appears  at  g ;  at  its  side  the  dorsal  wall  of  the  gut  shows  a  wide  contact  with 


DETAILS   OF    EARLY   EMBRYO. 


8l 


B 


Figs.  71  A-E  and  continued  F-I  on  page  82. — Transverse  sections  of  late  gastrula  shown  in  Plate  V,  fig.  36.     The  sections  pass 
forward  ;  the  first  of  the  series,  A,  traverses  the  tail  folds ;  the  last,  I,  the  head  region  of  the  early  embryo. 

fli  Tongue  of  mesoblast  cells  representing  the  urogenital  anlage ;  &,  megaspheres  in  process  of  passing  through  the  yolk-entoblast ;  be,  body  cavity; 
c.  points  in  extra-embryonic  region  where  the  ectoderm  cells  arc  being  proliferated  into  the  blastoderm  ;  a,  gut  cavity ;  m,  megasphere  appearing 
in  peristomial  mesoblast. 


82 


CHIM;EROID  FISHES  AND  THEIR  DEVELOPMENT. 


the  yolk,  and  here  at  various  points  yolk  nuclei  are  clustered,  having  evidently  an 
important  physiological  relation  with  the  overlying  blastoderm  ;  we  note  at  a  a 
tongue  of  mesoblast  cells  which  projects  medianward;  this  occurs  but  in  a  few 
sections,  and  evidently  corresponds  to  the  dark  area  noted  in  surface  view;  it 
resembles,  however,  so  closely  the  "lame  intermediate"  (Swaen  and  Brachet) 


H:   WVT.    -r^*^.- 

\i/    y    •        .»     »  •'-.  ^b 


Figs.  71  F-I.     (For  description  and  lettering  see  page  81,  A-E.) 

in  the  teleost,  that,  if  for  no  other  reason,  we  are  led  to  suggest  that  it  represents 
the  precocious  beginnings  of  the  excretory  system.  In  E  the  notochord  has  sepa- 
rated from  the  yolk,  the  gut  lumen  becomes  narrowed,  and  lateralward  the  first 
trace  of  a  body  cavity  (be)  appears.  We  observe  that  the  margin  of  the  gut 
passes  directly  into  yolk-entoderm,  the  distinctness  of  its  lower  boundary  having 


DETAILS  OF  EARLY  EMBRYO.  83 

faded  away,  and,  part  passu,  the  yolk  nuclei  have  greatly  increased  in  number.  In 
the  region  where  the  yolk-entoderm  approaches  the  lumen  of  the  gut  it  thickens 
and  sinks  downward,  leaving  as  the  floor  of  the  gut  cavity  a  wedge-shaped  mass  of  ger- 
minal yolk.  At  the  outer  rim  of  the  yolk-entoderm  we  observe  that  it  becomes  con- 
tinuous with  the  mesoblast;  in  other  words,  recalling  sections  D  and  G,  the  peristomial 
mesoblast  of  Chimaera  which  now  arises  is  not  continuous  with  the  gastral  mesoblast. 
We  have  thus  a  reason  for  inquiring  whether  gastral  and  peristomial  mesoblast 


Figs.  71  J-N.— Details  in  sections  of  foregoing  embryo  (figs.  71  A-I). 
/.  Region  of  peristomial  mesoblast. 

e,  ectoderm;  e',  cells  recently  derived  from  e  ;  entt  entodcrm  ;  m,  perutomiat  mesobiast. 
K.  Detail  of  subgerminal  yolk  region  showing  cellular  arrangement  of  merocyte  elements. 
L.  Lying  in  the  subgerminal  yolk  is  a  megasphere,  which,  on  the  evidence  of  the  overlying  vacuoles,  is  in  the  process  of  rising 

towards  the  yolk  entoderm. 

M.   Similar  megasphere  passing  into  the  yolk  entoderm. 
N.  Megaspheres  similar  to  preceding,  but  representing  a  somewhat  later  stage  of  passage  into  the  blastoderm. 

are  as  intimately  related  as  we  have  generally  assumed.*  A  condition  of  the 
peristomial  mesoblast  is  figured  in  detail  in  j,  and  it  proves  of  considerable  interest, 
since  the  region  of  mesoblast  proliferation  is  of  wide  extent.  Not  only  are  cells 
budded  out  from  the  marginal  mass  m,  but  we  observe  also  that  cells  are  added  to 
the  mesoblast  from  the  neighboring  ectoderm ;  thus  at  e'  is  a  cell  which  has  been 
derived  from  the  ectoderm  e,  where,  by  the  way,  a  syncytium  is  now  present ;  and 

*Cf.  the  current  view  as  to  the  secondary  confluence  of  blastopore  and  yolk   "  blastopore, "  as  summarized  in 
Ziegler's  Handbuch  der  Embryologie,  pp.  352  and  353. 


CHIlvLEROID   FISHES  AND  THEIR   DEVELOPMENT. 


at  the  point  e  a  mitosis  is  taking  place  preliminary  to  budding  off  another  mesoblast 
cell.  We  conclude  that  the  cell  e'  has  been  derived  from  the  layer  e,  and  not  from 
the  cell  mass  m,  when  we  consider  (i)  that  its  granular  contents  agree  in  character 
with  the  layer  e  rather  than  with  the  mass  m  ;  (2)  that  a  continuous  boundary  line  sepa- 
rates the  mass  m  from  e';  and  finally  (3)  that  the  cell  e'  is  connected  with  the  layer 
by  a  protoplasmic  process,  above  which  a  nucleus  in  mitosis  is  present.  Less 
evident,  from  this  section  at  least,  is  the  question  whether  cells  are  added  to  the 

0 


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Figs.  71  O-II. — Details  in  sections  of  foregoing  embryo  (continued  from  page  83). 

Detail  showing  transition  between  yolk  region  and  the  cells  of  the  blastoderm. 

m.  Yolk  nucleus  lying  against  the  wall  of  the  vacuole  «'.  "•  Zone  of  large  vacuoles. 

m'.  Yolk  nucleus  now  lying  within  a  vacuole,  and  transformed  into  V.  Zone  of  small  vacuoles  and  fine  germinal  yolk. 

a  yolk-surrounded  blastomerc.  3/C-  Yolk  enloderm. 

Detail  of  blastoderm,  showing  at  y  the  division  by  mitosis  of  a  megasphere  lying  in  the  yolk  entoderm. 
Detail  of  section  near  the  marginal  region  of  the  blastoderm,  showing  single  megasphere,  y,  lying  free  in  the  space  between 
ectoderm  and  yolk  entoderm. 
.'/«•  Yolk  nuclei  undergoing  division  by  atypical  mitosis  and  by  amitosis. 
R—II.     Details  showing  various  phases  of  division  in  yolk  nuclei. 

peristomial  mesoblast  from  the  entoderm  more  proximal  in  position.  At  some 
points  one  is  inclined  to  admit  that  such  a  cell  as  shown  in  j,  ent,  is  being  budded  off 
into  the  tongue  of  mesoblast.  (Cf.  the  condition  shown  in  the  section  N.) 

In  the  section  F,  the  notochord  is  again  continuous  with  the  entoderm;  the 
gut  region  rises,  and  its  lumen  is  now  walled  with  cells  save  in  its  median-ventral 
line.  Here  a  thin  wedge  of  yolk  intrudes.  Especially  noteworthy  is  the  relation 
of  the  yolk  to  the  yolk-entoderm  in  this  region.  The  latter  has  again  a  more 


MEROCYTES  AND  BLASTODERM.  85 

distinct  ventral  line  of  boundary,  broken  only  at  points,  as  at  b  and  b,  where  cells 
from  the  yolk  are  entering.  There  can  be  no  question  in  this  regard  since  the 
entering  cells  are  distinguishable  as  large  in  size,  circular  in  outline,  and  granular 
in  content.  (Cf.  sections  L,  M.)  Another  noteworthy  feature  in  this  section  is  that 
some  of  the  ectoderm  cells  as  at  c  and  c,  give  off  amoeboid  processes  and,  I  am 
led  to  believe,  later  become  detached,  contributing  to  the  growth  of  the  mesoblast. 
A  detail  of  this  condition  is  shown  in  section  j.  We  may  finally  note  that  the 
body  cavity,  be,  reaches  its  maximum  size  in  this  region  of  the  embryo. 

In  G  the  floor  of  the  gut  becomes  cellular  ;  the  notochord  is  again  separate  from 
the  gut  wall ;  and  as  before  merocytes  contribute  directly  to  the  growth  of  the  yolk 
entoderm.  In  n  the  last-mentioned  character  is  seen  even  to  better  advantage, 
for  not  only  are  the  large  yolk-cells  passed  into  the  lateral  yolk  entoderm,  but  they 
appear  also  high  up  in  the  central  gut  wall,  as  at^-,  and  in  the  region  of  the  peristo- 
mial  mesoblast,  as  at  m. 

In  i,  finally,  a  section  is  shown  passing  through  the  region  of  the  head  tip, 
which  now  projects  forward  above  the  blastoderm.  On  either  side  of  the  gut  the 
mesoblast  is  distinct,  differing  in  this  regard  from  the  condition  shown  in  an 
elasmobranch  (cf.  Ziegler's  figure  19,  n,  Arch.  f.  mikr.  Anat.,  Bd.  xxxix,  Taf.  iv). 
In  the  neighboring  blastoderm,  as  in  the  shark,  the  mesoblast  is  limited  to  a  small 
tongue  of  peristomial  cells. 

Before  concluding  an  account  of  this  stage  two  of  its  features  still  deserve 
comment,  (i)  The  fissuring  of  the  yolk  region.  The  fissures  are  usually  vertical, 
as  indicated  in  all  the  foregoing  sections,  and  may,  as  we  have  already  seen,  be 
regarded  as  homologous  with  cleavage  spaces.  (2)  The  mode  by  which  merocytes 
become  cells  of  the  embryo.  This  heading,  however,  deserves  to  be  treated  in  a 
more  formal  way. 

THE  TRANSFORMATION  OF  MEROCYTES  INTO  CELLS  OF  THE  BLASTODERM. 

In  this  connection  a  number  of  details  of  sections  of  stage  D  have  been  figured, 
figs.  71  K-II,  and  in  examining  the  series  we  find  evidence,  first  of  all,  that 
merocytes  move  from  a  lower  into  a  higher  zone  of  the  yolk.  Thus,  in  fig.  7 1  o,  the 
merocytes  are  elongated  in  the  direction  of  the  yolk-entoderm.*  Also  in  the 
three  sections  L,  M,  and  N  we  observe  a  great  yolk  cell  (megasphere)f  first  deep  in 

*That  this  is  connected  with  a  migration  of  these  elements  in  the  direction  of  the  surface  of  the  cell  mass  is 
known  by  analogy — witness  the  behavior  of  slime  cells  in  the  skin  of  amphibians  and  fishes  (e.  g.,  Homea). 

tThe  tnegaspheres  can  have  little  to  do  with  primitive  ova,  since  they  occur  widely  scattered  throughout  the 
blastoderm.  Thus  in  fig.  71  H  one  is  arising  at  the  extreme  rim  of  the  blastoderm,  in  F  several  are  seen  midway 
between  the  embryo  and  the  rim  of  the  blastoderm,  in  H  one  occurs  near  the  middle  of  the  floor  of  the  gut;  others 
appear  in  mesoderm  and  others  still  in  ectoderm.  In  these  several  regions  they  are  seen  to  undergo  division,  losing 
more  and  more  of  their  appearance  as  megaspheres  (v.  fig.  71  p).  It  can  not  be  believed,  therefore,  that  these  elements 
are  to  be  regarded  as  primitive  ova,  destined  to  carry  the  segregated  germ  plasm  into  the  embryonic  genital  folds,  for 
this  would  involve  a  conception  of  primitive  ova  traveling  about  extravagantly,  from  the  gut  wall  to  the  rim  of  the  blas- 
toderm, a  conception  the  more  improbable  when  we  consider  that  the  urogenital  region,  to  which  primitive  eggs 
naturally  belong,  is  already  indicated  by  this  stage,  as  at  a,  fig.  71  G.  On  the  other  hand,  it  follows,  I  believe,  that 
the  evidence  provided  by  Chimaera  strengthens  materially  the  position  of  Ruckert  that  the  megaspheres  in  elasmo- 
branchs  are  to  be  regarded  not  as  primitive  ova  but  as  highly  specialized  bearers  of  nutriment,  capable  of  carrying 
into  the  midst  of  embryonic  tissues  centers  of  new  formative  energy.  These  as  single  large  cells  could  be  passed 
through  the  intervening  tissue  more  effectively  than  could  the  many  small  cells  to  which  they  give  rise,  for  the  resistance 
of  an  embryonic  tissue  to  the  penetration  of  cells  is  obviously  proportioned  to  the  surface-contact  of  the  invading  cells. 


g6  CHIM^ROID   FISHES  AND  THEIR   DEVELOPMENT. 

the  germinal  wall,  next  having  just  emerged  from  the  germinal  wall,  and  finally 
having  almost  passed  through  the  niveau  of  the  yolk-entoderm.  We  have  even 
data  indicating  how  the  upward  migration  of  such  a  megasphere  takes  place.  One 
sees  in  L  a  line  of  vacuoles  appearing  between  the  megasphere  and  the  yolk- 
entoderm,  and  it  follows  clearly  that  the  vacuoles,  by  a  process  of  coalescence, 
provide  a  less  resisting  space  into  which  the  megasphere  can  rise. 

Regarding,  in  the  next  place,  the  fate  of  the  megaspheres,  I  think  that  there 
can  be  no  doubt  that  they  serve  to  bear  nutriment  to  the  tissue  which  they  enter. 
In  some  cases,  as  in  fig.  71  p,  at  y,  they  undergo  mitotic  division  (after  having  divided 
only  by  amitosis  in  the  yolk),  and  their  descendants  can  not  be  distinguished  from 
the  neighboring  cells.  In  other  cases,  M  and  N,  they  become  closely  surrounded 
by  cells,  entoderm  in  the  present  case,  which  form  around  them  a  syncytium,  and 
appear  to  serve  as  nutriment  distributors;  witness  for  example  the  grouping  of  the 
cells  around  the  large  megasphere  in  M,  and  the  radiating  arrangement  of  the  cells 
adjacent  to  the  cluster;  even  the  ectoderm  is  budding  off  a  cell  at  the  point  nearest 
the  megasphere. 

In  a  word,  I  think  we  can  fairly  conclude  that  in  Chimaera,  even  in  this  late 
stage,  cells  are  constantly  being  added  to  the  blastoderm  from  the  germinal  wall. 
This  condition  maintains  in  the  case  of  the  megaspheres,  as  we  have  just  noted, 
and  it  holds  equally  good  for  other  types  of  cellular  additions  to  the  blastoderm. 
We  thus  observe  in  o  (a  detail  of  section  G)  that  between  the  yolk-entoderm  (yc), 
and  the  wall  of  fine  yolk  (y)  is  a  vacuolar  zone,*  in  which  merocyte  elements  are 
being  ferried  over  to  become  cells  of  the  blastoderm;  thus  at  v'  is  a  vacuole  into 
which  the  merocyte  (m)  is  about  to  pass.  It  is  to  be  noted,  however,  that  cells 
may  also  appear  in  the  finer  yolk,  and  thence  by  the  mediation  of  an  enveloping 
vacuole  be  passed  upward  into  the  vacuolar  zone,  thence  to  the  blastoderm  (cf.  in 
fig.  710,  at  »/). 

That  throughout  these  stages  there  is  a  general  transformation  of  the  yolk 
from  coarser  elements  into  finer  elements  there  can  be  no  question.  Deep  in  the 
yolk  appear  nuclei  surrounded  by  spherical  masses  of  finer  yolk,  in  turn  surrounded 
by  masses  of  coarser  yolk,  in  turn  more  or  less  irregularly  by  a  system  of  vacuoles 
(=  intercellular  spaces)  fig.  71  K.  There  is,  to  be  sure,  a  greater  or  less  amount 
of  coalescence  of  these  yolk  elements,  and  in  the  zone  close  to  the  entoderm  we 
observe  that  the  nuclei  with  their  surrounding  fine  yolk  have  come  to  merge  into  a 
single  layer  (=  the  zone  of  merocytes  of  the  subgerminal  wall).  It  is  from  the 
elements  of  this  layer  in  turn  that  some  cellular  additions  to  the  blastoderm  are 
made. 

The  nuclear  changes  which  occur  during  the  process  of  their  "levitation"  are 
worthy  of  especial  comment,  for  while  the  cells  of  the  yolk-entoderm  now  divide  by 
mitosis  (as  in  o),  the  nuclei  of  the  region  below  the  vacuolar  zone  divide  amitotically, 

*Similar  conditions  have  been  observed  in  the  early  stages  of  teleosts  (cf.,  among  others,  Hoffmann,  Zeit.  wiss. 
Zool.,  vol.  XLVI  (1888),  pi.  xxxv,  a  paper,  by  the  way,  which  is  too  little  referred  to  in  recent  work  on  teleostean 
embryology). 


MEROCYTES  AND  BLASTODERM.  87 

and  under  varied  and  striking  forms — albeit  in  a  series  more  or  less  gradational 
(/.  e. ,  showing  more  decided  mitotic  character)  as  one  passes  from  a  lower  to  a 
higher  zone  in  the  yolk  substance.  To  illustrate  various  types  of  division:  In  R, 
in  a  sphere  of  fine  yolk  is  a  nucleus  about  to  divide  amitotically* ;  in  s  a  similar 
nucleus  has  undergone  such  a  division,  in  this  case  four  nuclei  resulting.  In  a 
somewhat  similar  case,  T,  noteworthy  growth  in  two  of  the  resultant  nuclei  has 
occurred;  they  have,  in  fact,  passed  out  of  the  sphere  of  finer  into  the  coarser 
yolk.  In  u  three  similar  and  large  nuclei  result.  _In  v,  which  represents  a  later 
stage  of  the  condition  shown  in  T  or  u,  and  is  drawn  similarly  from  deep  in  the  yolk 
region  of  a  section  (c.  g.,  as  seen  at  several  points  in  K),  continued  amitosis  occurs; 
here  one  of  the  larger  nuclei,  especially,  is  seen  to  be  budding  off  a  small  nucleus, 
and  it  has  already  apparently  budded  off  several.  In  w,  a  similar  detail  indicates 
the  great  rapidity  with  which  nuclei  may  arise;  a  large  nucleus  at  one  point  has 
given  off  a  small  one,  while  at  a  neighboring  point  almost  simultaneously  (judging 
from  the  close  position  of  the  small  nucleus)  it  is  budding  out  a  long  process  which 
is  about  to  be  separated  not  into  a  single  new  nucleus  but  into  two.  In  x  seven 
nuclei  have  arisen  from  a  single  center  (?  sphere  substance)  in  the  fine  yolk,  and  of 
these  one  has  undergone  rearrangement  in  its  chromatin  material.  Of  this  a  dense 
mass  occupies  the  center  of  the  nucleus  and  is  connected  with  the  nuclear  wall 
by  a  series  of  radiating  linin  strands.  In  Y  a  somewhat  similar  nucleus  is  shown  in 
detail;  at  one  side  it  is  apposed  to  the  finer  yolk  (=  ?  sphere  substance)  and  here 
the  mass  of  chromatin  approaches,  indeed  almost  touches  the  nuclear  membrane 
(for  nutritive  reasons?).  In  another  nucleus,  z,  the  chromatin  mass  shows  a  doubled 
arrangement,  preliminary,  as  it  appears,  to  a  stage  in  division  shown  in  AA,  FF,  and 
possibly  in  BE.  In  turn  the  doubled  nucleus  in  cc  is  obviously  a  further  stage  than 
AA,  but  it  shows  also  around  it  a  series  of  (five)  smaller  nuclei  which,  from  their 
radiating  arrangement  around  the  dividing  nucleus  in  the  center  of  the  fine  yolk, 
are  possibly  the  descendants  of  a  similar  type  of  nuclear  division.  In  DD  a  nucleus 
shows  a  less  distinct  doubling  of  its  chromatic  elements  than  AA-CC.  And  in  EE  a 
distinct  threefold  division  occurs.  GG  represents  a  stage  in  division  carried  further 
than  cc,  the  neighboring  nucleus  having  probably  arisen  from  a  similar  division. 
In  IIH  are  two  neighboring  nuclei,  the  products,  we  conclude,  of  a  division  like  that 
of  GG  and  cc :  but,  curiously  enough,  they  are  undergoing  division  in  different  ways. 
The  upper,  near  which  appears  an  attraction  sphere  and  centrosome,  has  arrayed 
its  chromatin  in  two  masses  nearly  equal  in  size,  each  suggesting  a  confused  series 
of  chromosomes;  the  lower  is  simply  passing  out  a  portion  of  its  chromatic  substance 
into  the  fine  yolk.  In  n,  the  last  of  the  series  given,  two  nuclei  appear;  they  are 
evidently  products  of  such  a  division  as  GG,  and  each  in  turn  is  about  to  undergo 
division.  The  lower  one  is  noteworthy,  since  the  division  of  the  chromatin  material 
is  practically  completed  in  the  middle  of  the  nucleus.  It  may  be  said  in  general 
that  the  nuclear  processes  which  here  approximate  mitosis  (cc  or  HH)  are  observed 
in  the  region  immediately  subjacent  to  the  yolk  entoderm. 

*A   similar   condition   in  the  embryonic   germ  cells  of   Loligo  appears   to   be   due  to  rapid  growth,    and    is   not 
followed  by  fragmentation  (Miss  Sturges,  Science,  1899,  Feb.  3,  pp.  183-184). 


gg  CHIM/EROID   FISHES  AND  THEIR  DEVELOPMENT. 

In  summary:  The  evidence  which  is  thus  provided  strengthens  the  conclusion 
that  in  the  gastrulation  of  Chimsera  amitosis  is  not  to  be  interpreted  in  accordance 
with  the  current  view,  i.  e.,  as  a  process  of  decadent  cell  division.  It  is  conditioned, 
rather,  by  rapid  growth  and  multiplication  of  nuclei,  since  its  products  may  resume 
mitosis  when  the  usual  rate  of  cellular  division  is  attained.  Moreover,  the  products  of 
amitotic  division  in  the  blastoderm  of  Chimsera,  are  too  many  and  too  widely  scat- 
tered to  warrant  the  belief  that  their  cellular  descendants  can  play  no  part  in 
producing  permanent  organs 

LATER  GASTRULA.     EMBRYO  WITH  PARTLY  CLOSED  MEDULLARY  FOLDS. 

This  stage  is  figured  in  surface  view,  plate  v,  fig.  37,  and  enlarged,  viewed  as 
a  transparent  object,  in  plate  vi,  fig.  41.  It  corresponds  approximately  with  Bal- 
four's  stage  F  in  the  shark. 

Comparing  the  blastoderm  of  this  with  the  preceding  stage,  we  find  that  it  has 
increased  but  little  in  size.  The  spongy  region,  however,  which  occupies  its  central 
portion  appears  more  prominently,  and  we  observe  a  noteworthy  thickening  in  the 
region  of  mesoblast  (gastral)  extending  outward  on  either  side  of  the  embryo.  The 
details  of  the  embryo  are  well  seen  in  a  toto  preparation.  The  medullary  folds  arch 
over  and  meet  in  the  median  line,  fusing  in  the  posterior  third  of  the  embryo's  length. 
In  front  of  this,  after  a  slight  interruption,  the  folds  meet  again,  then  diverge  to  a 
degree  suggesting  the  corresponding  stage  of  shark.  The  tail  folds  are  conspicuous 
at  this  stage,  and  we  observe  that  the  gut  has  arched  upward,  a  transverse  line 
showing  where  a  neurenteric  canal  is  to  open  below.  On  either  side  in  this  region 
the  mesoblast  is  thickened,  fading  away  laterally.  Here  are  forming  the  extensive 
caudal  veins.  Other  vascular  details  are  shown  in  the  antero-median  vessel 
(apparently  vitelline  vein)  which  appears  immediately  in  front  of  the  head  and 
spreads  out  widely  over  the  blood-producing  region.  We  note  also  transverse  larger 
vessels,  the  vitello-intestinal,  extending  outward  on  either  side  to  about  an  equal 
distance.  Gastral  mesoblast  is  conspicuous  in  this  stage;  in  this  may  be  traced 
about  a  dozen  somites,  the  anterior  ones  extending  far  forward. 

DETAILS  OF  FOREGOING  STAGE,  CORRESPONDING  TO  BALFOUR'S  STAGE  F. 

Sections  are  shown  in  fig.  72  A-E  passing  through  the  blastoderm  in  a  plane 
transverse  to  the  axis  of  the  embryo.  In  the  first,  which  passes  through  the  tail 
region  of  the  embryo,  we  observe  that  the  mesoblast  bands  (mes)  are  continuous 
with  the  entoderm  not  in  the  region  adjacent  to  the  notochord  but  marginally  (cf. 
the  view  of  Graham  Kerr  as  to  this  place  of  origin  in  the  vertebrate  gut  pouches); 
near  by  the  entoderm  (eni)  thickens  conspicuously,  then  thins  again  as  it  passes 
into  the  notochord.  Only  at  the  open  notch  between  the  tail  folds  does  the  lumen 
of  the  nerve  tube  pass  over  into  the  wide  space  (cf.  fig.  7 1  A)  which  is  coming  to 
form  the  cavity  of  the  gut.  It  will  be  seen  that  it  is  especially  the  thickening  of 
the  entoderm  and  the  constricted  origin  of  the  mesoderm  which  in  the  transparent 
preparation  (plate  vi,  fig.  41)  causes  the  appearance  of  a  dark  band  in  the  region  of 
the  tail  folds  of  the  embryo.  In  fig.  72  B  similar  conditions  in  gastral  mesoblast  and 


DETAILS  OF  EARLY  EMBRYO. 


89 


B 


Figs.  72  A  E. — Transverse  sections  and  details  of  the  blastoderm  shown  in  fig.  72.      The  sections  pass  anteriorward  from 
the  region  of  the  caudal  folds,  shown  in  section  A,  as  far  as  the  "neck"  region  of  the  embryo,  section  E. 

(I.  Beginnings  of  segmental  duct.  met.    Mesoderm. 

ect.  Ectoderm  at  the  point  where  this  becomes  continuous  with  the  !/.  Yollt  lying  free  in  the  gul  cavity. 

mesoderm  in  the  tail  folds  o(  the  embryo.  '     Urogenilal  anlage. 

'•"'•  Enloderm. 


90  CHIM^ROID   PISHES  AND  THEIR  DEVELOPMENT. 

entoderm  prevail;  the  thickened  ectoderm  at  ect  marks  a  point  at  which  this  layer 
is  making  cellular  additions  to  the  mesoblast;  it  represents  the  marginal  point 
where  the  tail  fold  and  the  margin  of  the  blastoderm  meet.  At  other  points  also, 
the  mesoblast  is  receiving  increments ;  in  addition  to  the  gastral  mesoblast  we  note 
cells  arising  from  the  wall  of  the  yolk-entoderm  midway  between  the  cavity  of  the 
gut  and  the  periphery  of  the  blastoderm,  and  we  see  further  that  an  invasion  of 


Figs.  72  F-K. — Details  of  the  region  of  the  yolk-entoderm  of  fig.  72.     In  /•'  the  region  is  indicated  in  detail  which  lies  immediately 
below  and  at  the  side  of  the  arching  wall  of  the  gut.     (Cf.  fig.  72  E.) 

"    Large  vacuolar   nucleus  which  appears  on  the  point  of  undergoing  reconstitution  Wl.  Megasphere. 

into  a  cell  of  the  yolk-entoderm.  SffZ.  Subgerminal  zone, 

ft.  Nucleus  similar  to  foregoing,  but  in  a  less  advanced  condition.  V.  Vacuolar  zone. 

r,  c',  (1.  Cells  which  have  recently  been  differentiated  out  of  the  germinal  wall.  ?/''-  Yolk  entoderm. 

G,  H,  and  I  illustrate  particularly  the  zone  of  reconstruction  of  yolk-entoblast  cells  from  yolk  nuclei.  In  J  a  telophase  occurs,  repre- 
senting a  rare  condition  in  the  subgerminal  zone.  In  K,  similarly,  a  telophase  occurs  in  a  megasphere.  The  latter  has,  however, 
passed  through  the  zone  of  vacuoles  and  lies  in  the  yolk-entoderm.  In  this  neighborhood,  however,  as  we  note  at  the  left,  a 
syncytial  condition  may  be  present. 

cells  from  the  periphery  of  the  blastoderm  has  occurred,  in  the  form  of  a  crease- 
shaped  invagination.  In  c  the  dorsal  wall  is  sharply  distinguished  from  the  sides  of 
the  gut.  On  the  floor  of  the  latter  appear  small  masses  of  yolk,  y,  which  can  only 
serve,  as  already  noted,  as  ingested  nutriment.  The  mesoblast  in  this  region 
shows  considerable  differentiation;  myotomes  are  sharply  marked  off;  the  gono- 


DETAILS   OF  EARLY   EMBRYO.  91 

nephrotomal  zone  is  of  notable  size;  at  d  and  in  the  adjacent  cell-mass  (at  the  left) 
are  the  beginnings  of  the  pronephric  tubules;  and  below  at  x  appears  the  thickening 
of  the  mesentoderm  whence  arises  the  posterior  portion  of  the  pronephric  duct. 

In  a  section,  D,  passing  through  a  more  anterior  region  of  the  embryo,  the 
urogenital  structures  are  practically  undifferentiated;  the  mesoblast  extending 
continuously  from  the  notochord  to  the  periphery  of  the  blastoderm.  In  this 
region  the  mesoblast  probably  receives  little  or  no  increment  from  the  yolk-ento- 
derm,  judging  from  the  latter 's  smooth  surface,  save  only  at  or  near  the  margin  of 
the  blastoderm.  Below  the  yolk-entoderm  in  this  region  the  subgerminal  zone  of 
nuclei  is  more  conspicuous  and  definite  than  in  the  early  stage,  fig.  71  E,  and  this 
zone,  indeed,  appears  with  even  greater  prominence  in  the  more  anterior  section, 
fig.  72  E  (to  be  contrasted  with  fig.  71  F  or  G).  It  will  here  also  be  seen  that  divi- 
sion of  the  mesoblast  into  splanchno-  and  somatopleure  is  occurring,  and  that  the 
lateral  wall  of  the  gut  is  more  definitely  established. 

A  detail,  shown  in  F,  indicates  the  more  special  relation  of  the  subgerminal 
zone  to  the  marginal  cells  of  the  gut  cavity.  The  subgerminal  zone  is  here  reduced 
to  a  narrow  tongue  (cf.  also  E),  which  inserts  itself  under  the  thickened  mass  of  cells 
at  the  base  of  the  gut  wall,  in  the  direction  of  the  lumen  of  the  gut.  In  the  present 
detail  the  base  of  the  gut  wall  is  shown  at  gw,  the  yolk-entoderm  at  ye,  the 
vacuolar  layer  at  v,  and  the  subgerminal  zone  at  sgz.  We  note  first  of  all  the  narrow- 
ness of  the  vacuolar  layer,  through  the  intervention  of  which  we  have  seen  (fig.  7 1  o) 
yolk  nuclei  become  cells  of  the  embryo,  a  condition  indicating  the  specialization  of 
this  region.  In  this  zone  (v),  furthermore,  we  see  large  nuclei  which  are  evidently 
in  transition  between  yolk  and  embryo,  and  at  m  a  megasphere  which  has  just 
passed  through  it,  the  vacuoles  becoming  reconstituted  below.  Most  significant  in 
the  region  of  the  rim  of  the  gut  wall  is  the  concentration  of  the  elements  of  the 
subgerminal  zone,  coarse  yolk,  fine  yolk,  lacunae,  vacuoles  and  yolk  nuclei  of  different 
kinds,  the  continuation  (to  the  left)  of  the  vacuolar  layer,  and  the  compounding  of 
its  vacuoles — characters  which  are  obviously  to  be  interpreted  as  more  special  and 
complicated  than  in  the  earlier  stage. 

A  few  additional  details  may  be  cited.  In  G,  where  nuclei  are  passing  through 
the  vacuolar  zone  and  becoming  cells,  we  observe  that  at  c  a  nucleus  which  has 
been  taken  into  a  large  vacuole  (a  process  forming  now  a  reconstituted  cell),  is  still 
dividing  amitotically,  and  that  at  c'  a  similar  division  has  recently  occurred,  indi- 
cating in  both  cases,  as  we  have  before  remarked,  that  the  difference  between  ami- 
totic  and  mitotic  division  is  one  of  degree  rather  than  of  kind.  In  H,  a  detail  from 
a  section  close  to  fig.  72  E,  a  point  is  figured  where  merocytes  and  newly  constituted 
yolk-entoderm  cells  occur  in  such  confusion  that  it  is  difficult  to  say  where  the  layer 
of  merocytes  terminates  and  where  the  cells  of  the  embryo  begin.  And  the  same 
is  true  of  the  detail  shown  in  i.  In  the  last  figure,  on  the  other  hand,  merocytes 
are  still  multiplying,  even  at  a  point  close  to  the  yolk-entoderm.  In  j,  a  detail  of 
the  vacuolar  region,  cells  are  arising  from  merocytes;  at  b  a  merocyte,  less  vesicular 
than  «,  adjoins  a  vacuole  into  which  it  will  probably  pass,  judging  from  transitional 
conditions  (cf.  the  neighboring  c).  And  even  in  the  vacuolar  layer  such  newly 


92  CHIM^.ROID   FISHES  AND  THEIR   DEVELOPMENT. 

constituted  cells  may  divide,  and  by  mitosis,  although  this  is  not  of  the  usual  type 
(cf.  at^).  In  this  connection,  finally,  in  K  a  detail  is  given  showing  that  megaspheres 
as  they  pass  into  the  yolk-entoderm  present  more  or  less  evident  mitosis,  witness 
the  conditions  m  and  m  (cf.  also  fig.  72  F  at  m).  Parenthetically,  just  below  the 
megaspheres  here  mentioned  are  vacuoles  into  which  merocytes  are  passing. 

EARLY  EMBRYOS  FROM  THE  COMPLETE  CLOSURE  OF  MEDULLARY  FOLDS 
TO  OPENING   OF   GILL-CLEFTS. 

An  early  embryo  attached  to  its  blastoderm  is  shown  in  plate  v,  fig.  38.  This 
may  be  contrasted  with  the  stage  of  closing  medullary  folds  shown  in  same  plate, 
fig.  37.  In  the  blastoderm  we  observe  that  the  spongy  central  area  has  increased 
notably  in  size  and  that  it  has  even  extended  to  the  anterior  rim  of  the  blastoderm. 
We  note  also  that  asymmetry  has  made  its  appearance,  the  embryo  now  lying  some- 
what on  its  right  side.  The  present  blastoderm  has  increased  more  rapidly  at  its 
left,  and  here  a  lobe-like  eminence  is  produced  hindward  over  the  yolk.  The 
entire  size  of  the  blastoderm  is  scarcely  larger  than  in  the  preceding  figure.  The 
embryo  is  shown  in  detail,  plate  vi,  as  an  opaque,  fig.  41",  and  then  as  a  transpar- 
ent object,  fig.  4ib.  In  general  this  stage  corresponds  with  Balfour's  stage  G  in 
shark;  it  differs,  however,  in  the  definiteness  of  its  structures,  for  the  anterior  region 
has  already  become  quite  highly  differentiated  in  spite  of  the  fact  that  the  tail  region 
is  still  flattened  out  against  the  yolk  and  hardly  protrudes  beyond  the  rim  of  the 
blastoderm.  About  22  segments  are  present  in  this  stage.  The  head  rises  above 
the  blastoderm  and  the  divisions  of  the  brain  and  the  optic  vesicles  are  formed,  and 
it  is  an  evidence  of  the  high  specialization  in  development  that  the  embryo  of 
this  large-eyed  form  should  possess  large  optic  vesicles  at  this  early  period,  i.  e., 
before  the  tail  end  of  the  body  is  established, — a  fact  of  considerable  interest 
from  the  standpoint  of  embryonic  adaptation.  In  this  stage  two  gill-slits  are 
appearing,  g3,  g".  The  region  of  the  pronephros  is  marked  out  at  pn,  the  heart  at 
h,  the  anterior  cardinal  vessels  at  c,  and  the  vitello-intestinal  at  o.  In  the  tail  region 
the  neurenteric  canal  is  distinctly  seen  at  n. 

DETAILS  OF   THE  PRESENT  EMBRYO  (STAGE  G). 

A  series  of  selected  transverse  sections  of  this  embryo  may  now  be  passed  in 
review  to  indicate  the  more  prominent  advances,  figs.  73  A-UU.  The  anterior 
sections  A-D  pass  through  the  ectoderm  inclosing  the  tip  of  the  head  and  show  a 
conspicuous  median  infolding  (recessus  olfactorius  impar)  which  in  surface  view 
gives  the  appearance  of  separating  a  "forebrain"  from  a  "right  optic  vesicle,"  the 
sections  having  been  cut  in  the  plane  indicated  by  the  dotted  line  in  plate  vi,  fig.  4ib. 
The  next  section  (E)  touches  the  distinct  end  of  the  central  nervous  system,  the  wall 
of  which  is  more  extensively  traversed  in  F  and  G.  In  H,  i,  and  j,  the  lumen  of  the 
forebrain  is  traversed.  In  K  and  L,  representing  many  sections,  the  cavities  of 
the  optic  vesicles  appear,  and  we  observe  here  closely  apposed  to  the  ventro- 
median  wall  of  the  brain  a  mass  of  cells  which  in  later  sections  is  seen  to  constitute 
the  anterior  end  of  both  notochord  and  gut.  In  sections  M  and  N  this  cell  mass  forms 
a  conspicuous  ventral  keel,  in  N  the  lumen  of  the  gut  first  appearing.  In  o  and  p 


DETAILS   OF   EARLY   EMBRYO. 


93 


F 


H 


Figs.  73  AS. — Transverse  sections  of  embryo  shown  in  plate  V,  fig.  38,  and  in  plate  VI,  figs.  41  and  41  A.     These  begin  at  the 
head  end  of  the  embryo,  section  A,  and  extend  through  47  sections  to  the  tip  of  the  tail,  section  UU  (see  pages  94  and  95.) 
fft  Gut  cavity;  n,  notochord;  *i  somite. 


CHIM^ROID  FISHES  AND  THEIR   DEVELOPMENT. 


cc 


DD 


be.     Body  cavity. 
(/' .  .</"•      Evagination  of  gut  wall  to  form  the 

first  and  second  sill  openings. 
/>.     Heart. 


Figs.  73  T-EE — Continued. 

nc.    Neural  crest, 
in.     Subnotochordal  rod. 
y.    Yolk  lying  free  in  cavity  of  gut. 


DETAILS   OF   EARLY   EMBRYO. 


95 


r\ 


HH 


Figs.  73  FF-UU.— Continued. 
w.  Wedge-shaped  mast  of  yolk  which  cornel  to  pass  into  the  ventral  wall  of  the  gut  cavity. 


96 


CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 


we  distinguish  in  this  ventral  cell  mass  a  lower  lumen-bearing  area  and  above  a 
thickened  mass,  on  either  side  of  which,  attached  but  not  fused,  lies  a  solid  mass  of 
mesoblast.  In  Q  we  distinguish  notochord  and  gut  (»,  g};  on  either  side  of  the 
notochord  the  mesoblastic  somite  (s)  bears  a  cavity.  In  R  the  mesoblastic  sacs 
are  well  separated  from  both  notochord  and  gut,  and  the  notochord  itself,  greatly 
reduced  in  size,  shows  a  compressed  and  almost  longitudinally  subdivided  appear- 
ance. In  s,  the  body  of  the  embryo  is  becoming  flattened  on  its  side;  the  lumen  of 
the  gut  is  deep  and  narrow;  closely  apposed  to  its  sides  are  the  mesoblastic  masses 
whose  lumen  now  becomes  greatly  reduced ;  on  the  dorsal  median  wall  of  the  gut 
appear  the  beginnings  of  a  subnotochordal  rod.  From  this  stage  onward  the  lumen 
of  the  central  nervous  system  becomes  notably  reduced.  In  T  the  section  passes 
through  the  embryo  in  the  plane  where  the  neck  region  flattens  out  over  the  yolk. 
Here  we  note  the  distinct  subnotochordal  rod  (sn)  and  the  flattening  mesoblast 
which  now  forms  a  delicate  band  almost  surrounding  the  gut.  In  the  surface  view  of 
this  region,  on  the  other  hand,  only  the  thickened  proximal  ends  of  the  mesoblast 
masses  can  be  distinguished.  In  u,  where  the  neck  is  flattened  out,  the  heart 
appears  at  h;  and  in  the  upper  region  of  the  gut  we  note  the  thickening  of  the  wall 
of  the  gill-slit,  the  cavity  of  which  is  seen  in  the  preceding  section  at^1.  In  v,  as 
indeed  in  some  of  the  earlier  sections,  a  thickened  neural  crest  appears  at  nc.  In 
w  the  body  cavity  (be)  is  becoming  conspicuous.  In  x  the  somato-  and  splanchno- 
pleure  spread  out  widely  peripherally;  in  the  gut  we  notice  in  the  thickening  of  the 
lateral  walls  an  out-bending  for  the  second  gill-slit  (cf.  in  z,  g11)  and  in  the  cavity  of 
the  gut  in  this  and  in  many  sections  following  we  find  masses  of  yolk.  These 
masses,  sometimes  small,  as  in  sections  z,  AA,  BB,  EE,  sometimes  large,  as  in  Y,  cc, 
DD,  are  unquestionably  budded  out  (as  in  EE  and  HH)  of  the  ventro-median  wall  of 
the  gut.  On  account  of  their  abundance  and  range  in  size  we  can  not  conclude 
that  they  are  artifacts,  but,  on  the  other  hand,  if  we  regard  them  as  normal 
structures,  it  is  natural  to  assume  that  they  serve  as  food  material,  and  are  assimi- 
lated by  the  gut  in  the  usual  way.  This  conclusion,  simple  as  it  seems,  is  none  the 
less  difficult,  since  it  attributes  to  Chimaera  an  embryological  process  which  appears 
to  be  unknown  in  the  vertebrata  and  only  remotely  paralleled  among  invertebrates. 
If,  accordingly,  we  accept  the  present  evidence,  it  follows  that  Chimaera  is  to  be 
regarded  as  the  terminal  member  of  an  evolutional  series,  at  one  end  of  which  were 
forms  whose  yolk-laden  cells  contributed  directly  to  the  growth  of  the  young;  next 
came  those  whose  yolk-filled  cells  contributed  indirectly  to  the  growth  of  the  young 
through  various  processes,  typically  through  the  intervention  of  merocytes;  and 
finally,  in  Chimsera,  the  mode  of  nutrition  by  merocytes  is  supplemented  by  a  still 
more  oblique  process,  i.  e.,  one  which  passes  fragmented  yolk  material  from  the 
zone  of  merocytes  directly  into  the  lumen  of  the  gut. 

Continuing  the  sections:  In  GG,  and  in  many  sections  following,  a  wedge-shaped 
mass  of  yolk  material  (w)  is  converging  toward  the  ventro-median  line  of  the  gut 
(v.  also  p.  76);  in  LL  it  becomes  subdivided,  and  in  MM  appears  a  small  recess  which 
may  also  contain  this  nutriment  (?  anlage  of  liver).  In  jj  and  in  following 


YOLK    AND    YOLK-ENTODERM    IN    EARLY    EMBRYO. 


97 


sections  the  pronephric  duct  appears,  at  first  only  on  the  left  side,  as  an  ectodermal 
keel,  beginning  about  the  plane  of  the  8th  somite.  Thence,  passing  backward,  it 
merges  with  the  somatopleure  at  about  the  plane  of  the  1 2th  somite,  after  MM.  In 
this  section  the  subnotochordal  rod  appears  for  the  last  time.  In  oo  the  notochord 
dips  into  the  dorsal  wall  of  the  gut;  and  in  PP  it  forms  an  evagination  of  its  wall. 
QQ  and  RR  are  sections  through  the  neurenteric  canal,  and  ss  to  uu  through  the 
tail  end. 

Two  further  details  of  this  stage  are  shown  "in  figures  74  and  75.  The 
former  of  a  section  close  to  that  of  fig.  73  LL,  the  latter  from  a  section  close  to  fig. 
73  G,  representing  only  a  detail  of  the  extra-embryonic  blastoderm  lying  under  the 
region  of  the  head.  Fig.  74  has  been  given  to  illustrate  the  ingress  of  yolk  material 
through  the  ventral  wall  of  the  gut,  for  here  is  seen  the  wedge  of  yolk  protruding 
through  the  thickened  mass  of  yolk-entoderm  cells,  but  under  conditions  which 
bespeak  the  complicated  nature  of  the  process.  For  the  rest,  there  is  here  not  a 
mere  rupture  which  admits  the  yolk  into  the  cavity  of  the  gut,  but  an  attendant 


Fig.  74. — Detail  of  section  of  early  embryo  shown  in  fig.  73  LL. 
y.  Yolk  plug  pressing  into  cavity  o(  gut ;  V'.y",v"',  layers  of  yolk  of  different  consistencies. 

series  of  changes  of  which  the  "rupture"  itself  is,  with  fair  probability,  the  terminal 
member.  Thus  the  wedge-shaped  mass  of  yolk  (y)  is  composed  of  fine  yolk;  it 
next  passes  through  a  transitional  zone  (_/)  into  the  coarse  yolk  (y").  And  on 
either  side  of  the  wedge  lies  a  layer  of  very  coarse  yolk  (j/"),  which  obviously  comes 
into  close  physiological  rapport  with  the  neighboring  layers,  for  this  thickens  as  it 
approaches  the,.yolk-wedge,  and  here  it  is  filled  with  nuclei  of  extraordinary  size. 
Indeed  on  one,  side  (left)  we  note  that  this  layer  of  coarse  yolk  is  separated  from  the 
yolk-entoderm  by  a  layer-like  offshoot  of  the  fine  yolk  (j/)  from  near  the  point  of 
the  wedge.  We  observe  also  the  relation  which  the  bordering  yolk-entoderm  bears 
to  the  point  of  the  yolk-wedge,  for  this  layer  is  here  many  times  thicker  than  in 
neighboring  regions.  The  yolk-wedge,  in  short,  which  passes  into  the  cavity  of 
the  gut  stands  in  specialized  relation  (i)  to  the  usual  mass  of  yolk,  i.  e.,  spreading  out 
fan-shaped  below,  thus  securing  a  large  surface  of  contact;  (2)  to  the  lateral  areas 
of  coarse  yolk;  (3)  to  the  lateral  masses  of  yolk-entoblast,  and  (4)  finally,  as  we 


98 


CHIM^ROID    FISHES    AND    THEIR  DEVELOPMENT. 


Fig.  75. — Detail  of  extra-embryonic  region  of  embryo  of  fig.  73. 
«.  Ectoderm;  m,  maoblut ;  meg,  meg',  gigantic  yolk-cells  ;  »,  vacuole; 
,V<  i  yolk-entoderm. 


have  already  seen,  to  the  walls  of  the  gut,  since  it  passes  to  them  yolk  masses, 
large  and  small,  and  perhaps  also  dissolved  yolk  material.  In  evidence  of  the 
nutritive  value  of  this  material  witness  numerous  mitoses  in  the  adjacent  (inmost) 
cells  of  the  entoderm — one  of  which  appears  in  the  present  section. 

In  fig.  75  a  detail  is  given  of  the 
process  by  which  yolk-cells  are  passed 
into  the  tissues  of  the  embryo.  In  this 
portion  of  the  extra-embryonic  blasto- 
derm the  mesoderm  occurs  only  as 
detached  (mesenchymatous)  cells  (m); 
the  ectoderm  forms  a  single-celled 
layer,  and  the  entoderm  a  closely 
formed  cellular  mass  (j'e).  Between 
the  entoderm  and  the  yolk  is  the  usual 
zone  of  vacuoles  (v).  At  meg  a  large 
yolk-filled  cell  (cf.  pp.  83  et  seq.)  pro- 
trudes from  the  yolk  into  the  entoderm, 
the  cells  of  the  latter  affording  little  bar 
to  its  progress  upward.  In  this  connection  we  note  that  the  huge  cell  (meg)  lies 
now  within  a  vacuole  in  whose  wall  yolk-nuclei  appear;  indeed  at  one  point  a  yolk- 
nucleus  has  actually  entered  the  vacuole.  In  the  same  figure  at  meg'  is  a  large 
cell  (cut  not  quite  through  the  middle)  which  has  evidently  had  a  similar  origin  to 
meg;  for  from  its  size  it  can  not  be  confused  with  a  neighboring  cell  of  any  germ 
layer.  It  contains  coarse  yolk,  and  on  account  of  its  irregular  outline,  judging  from 
earlier  instances,  it  has  probably  undergone  division  by  amitosis. 

ADDITIONAL  EMBRYOS  OF  THIS  PERIOD. 

A  second  embryo  of  this  period,  i.  e.,  prior  to  the  breaking  through  of  gills 
and  mouth,  is  shown  on  plate  vn,  figs.  42,  42"  and  42**,  and  on  plate  vni,  fig.  42°. 
The  present  specimen  is  badly  bent  in  its  trunk  region,  but  in  other  regards  it  may 
be  readily  compared  with  the  earlier  stage,  plate  vi,  fig.  41.  The  chief  advances 
include:  (i)  the  modeling  of  the  trunk,  in  whose  hindmost  region  only  appears  the 
former  flattened  condition;  (2)  the  appearance  of  auditory  sacs  (««);  (3)  the  model- 
ing of  optic  vesicles  (pp)\  the  protrusion  of  the  forebrain  region  into  a  frontal  knob 
(£).  The  general  shape  of  the  head,  as  shown  in  dorsal  view,  already  suggests  the 
adult  condition,  in  spite  of  the  small  size  of  the  embryo.  This  noj^  measures  only 
2. 5  mm. ,  not  allowing  for  the  bent  trunk  region.  The  tail  at  this  stage  protrudes 
beyond  the  rim  of  the  blastoderm,  its  tip  budding  out  like  a  knob  beyond  the  flat- 
tened caudal  eminence.  About  25  somites  are  present. 

A  third  embryo,  plate  vn,  figs.  43  and  43",  shows  over  sixty  somites,  and 
gives  us  a  picture  of  the  young  Chimaera  at  about  the  end  of  the  first  month  of 
incubation.  In  this  stage  over  sixty  somites  are  present,  and  the  tail  bud  has 


EARLY   EMBRYOS.  99 

grown  out  conspicuously.  The  broad  flattened  trunk  terminal  of  the  preceding 
embryo  is  here  represented,  and  at  a  the  anal  region,  a  point  anterior  to  which  the 
number  of  somites  corresponds  in  a  general  way  to  that  in  the  earlier  stage. 
Noteworthy  advances  include: 

(1)  A  more  definite  modeling  of  the  regions  of  head  and  trunk.     The  latter 
has  now  lifted  up  above  the  surrounding  blastoderm,  and  the  head  (including  the 
chin  region)  has  separated  from  the  yolk-wall. 

(2)  The  gill-slits  are  now  conspicuous,  although,  as  sections  show,  they  have 
not  yet  broken  through;  we  note  that  the  spiracular  slit  s,  evidently  the  equivalent 
of  g1  in  the  former  stage,  is  of  considerable  size;  behind  it  occur  three  prominent 
depressions  and  the  trace  of  fourth  and  fifth. 

(3)  The  appearance  of  pronephros  and  pronephric  duct;  the  pronephros  itself  is 
situated  at  the  plane  of  the  ninth,   tenth,  eleventh  and  twelfth  somites,   as  can 
better  be  seen  in  the  transparent  preparation  in  the  same  embryo,  plate  vn,  fig.  43°. 

(4)  The  knob-like  terminal  eminence  of  the  head  region  has  greatly  increased 
in  size. 

A  fourth  embryo  of  this  period  is  shown  as  a  transparent  preparation  in  plate 
vir,  fig.  44.  It  contains  a  greater  number  of  somites  than  the  preceding,  over  80 
as  opposed  to  over  60,  but  in  many  regards  it  appears  to  be  less  advanced  in  devel- 
opment. Thus  we  note  that  its  head  region  appears  somewhat  less  mature  than  in 
the  former  embryo;  the  chin  is  less  definitely  established  and  so  also  the  gill-slits 
are  shallower  and  the  optic  and  auditory  vesicles  and  the  pronephros  less  definite. 
The  tail,  moreover,  is  less  pointed,  even  bulbous  where  the  terminal  growth  is  taking 
place.  In  this  stage  we  note  the  presence  of  a  conspicuous  postanal  gut.  The 
details  of  the  vascular  supply  of  the  gill  region  are  well  shown ;  the  spiracular  artery 
is  conspicuous,  and,  further  hindward,  we  observe  the  duct  of  the  pronephros  (pnd) 
and  the  postanal  gut  pag. 

A  series  of  characteristic  sections  of  this  stage  is  given  in  figures  76  A-N. 
These  show  a  general  correspondence  to  the  conditions  of  the  young  shark.  In 
fig.  c  the  premandibular  head  cavity  (pm)  is  shown;  in  D  the  mandibular  (m).  In 
this  section  also  we  observe  that  the  mouth  has  not  yet  broken  through.  In  later 
sections,  as  in  E,  F,  H,  i,  and  K,  we  note  that  the  gill-slits  have  not  been  com- 
pleted; fusions  of  the  gut  wall  with  the  ectoderm  have,  however,  occurred.  We 
note  in  section  M,  passing  through  the  pronephric  tubules,  that  the  relation  of  these 
structures  corresponds  closely  to  that  in  the  young  shark.  A  subnotochordal  rod, 
conspicuous  in  the  earlier  stage,  is  here  represented  only  in  a  rudimentary  condition, 
as  in  N  ;  the  gut  has  separated  from  the  notochord  and  the  main  vascular  trunks  now 
appear  in  the  region  formerly  occupied  by  the  subnotochordal  rod.  The  present 
stage  corresponds  closely  with  that  of  the  shark  in  which  the  mesoblast  bounds  a 
continuous  myo-,  nephro-,  and  splanchno-ccele.  In  Chimera,  however,  continuity 
in  these  regions  is  less  clearly  marked,  a  feature  which  evinces  greater  develop- 
mental specialization,  i.  e. ,  in  masking  an  archaic  condition  and  preparing  the  way 
for  the  prompter  growth  of  structures  useful  to  the  young  fish. 


100 


CHIM^EROID   FISHES  AND  THEIR   DEVELOPMENT. 

THE  RELATION  OF   THE  BLASTODERM  AND   YOLK  AT  THIS   STAGE. 


As  already  noted  (p.  58),  the  egg  of  Chimaera  has  by  this  time  undergone  a 
process  of  fragmentation.  The  bulk  of  the  egg  subdivides  in  the  direction  of  pro- 
ducing for  the  embryo  nutriment  to  be  appropriated  via  gills  and  gut;  a  single  mass 


Fig*-  76  A-N. — Transverse  sections  of  the  embryo  shown  in  plate  VII,  fig.  44. 
Wl,  Mandibular  head  cavity  ;  /"'* ,  premandibular  head  cavity. 


YOLK-SAC     OF    EARLY    EMBRYO. 


IOI 


only,  representing  about  one-tenth  the  bulk  of  the  unsegmented  egg,  is  reserved 
for  the  yolk-sac  of  the  young  fish. 

In  the  stage  last  described  (i.  e.,  of  plate  vn,  fig.  44),  in  spite  of  the  advanced 
characters  of  the  embryo,  the  blastoderm  has  not  increased  vastly  in  size  beyond 
that  shown  in  plate  v,  fig.  38.  It  has,  however,  as  we  see  in  plate  vm,  fig.  47, 
constricted  marginally,  becoming  cup-shaped,  as  it  continues. to  envelop  the  small 
yolk  mass.  How  far  it  has  succeeded  in  inclosing  the  yolk  'is:  p'erhaps  better  seen 
in  the  details  of  the  last  figure,  shown  in  figs.  47a_and  47b/  '  /,  :  '•'•'.'•'">'•.','  ':'•''.  ''.  A 

The  relation  of  yolk  and  blastoderm  is  pictured  in  detail"  in  fig.  77, 'a  section 
passing  through  the  blastoderm  parallel  to  the  long  axis  of  the  embryo.  At  the 
points  mb  and  mb',  the  rim  of  the  blastoderm  comes  in  contact  with  the  yolk ; 
above  mb  the  blastoderm  is  thickened  and 
spongy;  for,  as  a  sign  that  the  body  of  the 
embryo  lay  adjacent,  this  region  is  richly 
vascular.  Noteworthy  here  is  a  deep  sub- 
marginal  sinus  (ms)  whose  posterior  wall  (c) 
is  cellular.  We  have  in  this  condition  a 
physiological  parallel  with  the  submarginal 
space  in  ganoids,  and  more  directly  even  with 
Kupffer's  vesicle  in  teleosts.  On  the  ventral 
side  of  the  blastodermic  cap  (on  the  left  in 
the  figure)  the  vascular  sponginess  is  largely 
lost ;  and  the  blastoderm  is  thin,  save  only  at 
its  rim  (mb').  And  here  in  place  of  a  deep 
submarginal  sinus,  a  number  of  distinct  blood- 
producing  vesicles  appear  (ms)  scattered 
distally  in  a  narrow  zone  of  finely  divided  yolk  (fy).  From  another  standpoint, 
finally,  the  present  section  is  noteworthy.  For  it  shows  that  the  entire  yolk-sac  is 
divided  into  masses  which  are  largely  separated  from  one  another  by  a  system 
of  fissure-like  vacuoles.  Closer  inspection  shows  nuclei  scattered  irregularly 
through  these  masses  of  yolk,  and,  everything  considered,  I  think  we  can  therefore 
justly  conclude  that  the  yolk-sac  at  this  stage,  in  spite  of  its  relatively  large  size,  is  a 
totally  segmented  structure  comparable  with  the  yolk-sac  of  Amia  or  Ichthyophis. 
In  the  present  case,  it  is  true,  the  yolk  masses  (blastomeres)  show  a  condition  of 
greater  or  less  attachment  to  their  neighbors,  and  each  mass  will  usually  contain 
more  than  a  single  nucleus.  But  even  in  this  event,  the  comparison  will,  I  believe, 
hold.  In  some  cases  the  shape  of  the  yolk  masses  is  distinctly  blastomere-like, 
as  between  the  vacuoles  (v)  in  the  present  section.  Viewed  from  this  standpoint, 
accordingly,  Chimsera  has  retained  a  primitive  embryological  character,  holoblastic 
cleavage;  but  we  can  hardly  fail  to  observe  that  this  character  has  lost  much  of  its 
primitiveness  inasmuch  as  the  blastomeres  are  polynuclear  and  the  intercellular 
spaces  obviously  adapted  as  reservoirs  of  nutriment. 


Fig.  77.—  Section  of  extra-embryonic  region  and  of  upper 
part  of  yolk-sac  of  stage  of  plate  VIII,  fig.  47. 

c.  Cellular  area ;  mb,  mb',  margin  of  blastoderm:  ms,  marginal 
sinus  ;  /.'/i  fluid  yolk  ;  V,  vacuoles. 


I02  CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 

LATE  EMBRYOS. 
EMBRYOS  FROM  THE  APPEARANCE  OF  GILL-OPENINGS  TO  THE  TIME  OF  HATCHING. 

Four  specimens  illustrating  this  period  are  described  on  the  following  pages. 
The  first  of  these,  shown  in  toto  (plate  vn,  fig.  45),  illustrates  a  stage  in  which  all 
five  gill-slits  are  cle.arly  shown,  but  of  these  only  the  first  has  completely  broken 
through,  tha,t  lying  immediately  below  the  auditory  vesicle.  In  front  of  this  the 
spiracular  cleft  is  faintly  outlined.  The  entire  head  region  is  modeled  clearly,  and 
the  anterior  "end  of  the -embryo  has  separated  from  the  blastoderm  as  far  back  as 
the  region  immediately  behind  the  heart.  The  tail  has  greatly  elongated  and  has 
entirely  lost  the  bulbous  terminal  which  we  noted  in  the  earlier  embryo. 

The  region  immediately  adjacent  to  the  embryo  is  divided  up  into  a  spongy 
mass  by  many  blood-vessels;  we  observe  also  that  the  blastoderm  has  almost  com- 
pletely inclosed  the  attached  yolk  mass,  a  small  yolk  plug  only  being  visible  at  the 
hinder  end  of  the  yolk-sac.  This  condition  is  shown  in  plate  vm,  fig.  48.  Here, 
through  the  rim  of  the  blastoderm  one  can  faintly  see  the  extent  of  the  submarginal 
sinus  which  was  noted  in  the  preceding  stage.  From  it  now  extend  many  vessels, 
as  indicated  in  the  figure.  The  region  of  the  yolk  plug  is  figured  in  plate  vm, 
fig.  48",  as  viewed  under  a  dissecting  microscope.  It  shows  an  interesting  condition 
in  connection  with  the  holoblastic  behavior  of  the  yolk;  for  a  number  of  irregular 
masses  are  visible,  outlined,  it  appears,  by  vacuoles,  and  suggest  yolk-filled  blasto- 
meres.  It  will  be  observed,  however,  that  the  contours  of  the  yolk  masses  are  less 
definite  as  they  approach  the  irregular  rim  of  the  blastoderm.  (Cf.  fig.  77.) 

Sections  of  this  stage  are  shown  in  the  adjacent  figures.  In  the  first  (fig.  78) 
the  mouth  (i.  e.,  its  hinder  portion)  and  auditory  vesicles  are  traversed;  the  mouth 
has  not  yet  broken  through  nor  has  the  neighboring  gill-slit,  the  hyomandibular. 
We  note  that  the  auditory  vesicle  is  now  a  thick-walled  sac  opening  broadly  at  the 
surface;  that  a  subnotochordal  rod  is  present;  that  the  brain  wall  in  this  region  (hind- 
brain)  is  remarkably  thick  and  asymmetrical,  and  that  the  fifth  ventricle  is  corre- 
spondingly reduced  in  diameter.  A  section  through  the  mid-trunk  (fig.  79)  indicates 
that  in  this  region  the  trunk  is  spread  out  more  widely  than  in  the  corresponding 
or,  in  fact,  in  any  stage  in  the  shark.  The  splanchnocoele  (spc)  is  of  great  size,  and 
its  walls,  both  splanchnic  and  somatic,  contain  large  spaces.  The  myocoele  is 
virtually  obliterated,  although  its  margining  cells  have  not  fused  across  its  earlier 
opening  into  the  gononephrocrele.  The  last  region  is  not  clearly  demarked;  atpn  a 
pronephric  tubule  appears  in  the  position  usual  in  elasmobranch.  At  df  the  early 
condition  of  the  dorsal  fin  corresponds  closely  with  that  of  a  shark  embryo. 

A  second  embryo  (plate  vn,  fig.  46)  slightly  older  than  the  preceding,  was  one 
of  the  specimens  received  from  Dr.  Wilbur.  It  had  with  it  only  a  small  fragment 
of  the  blastoderm,  and  at  the  time  of  preservation  the  embryo  appears  to  have 
turned  in  a  position  nearly  transverse  to  its  usual  one.  At  this  stage  the  tail 
protruded  widely  over  the  rim  of  the  blastoderm,  and  it  follows,  therefore,  that, 
probably  as  an  individual  variation,  the  blastoderm  has  not  as  completely  inclosed 


DETAILS   OF   LATER   EMBRYO. 


103 


the  yolk  as  in  the  former  specimen.  A  more  detailed  examination  of  this  embryo 
shows  that  two  gill-slits  have  broken  through.  The  mouth,  moreover,  is  more  nearly 
completed,  the  mandible  appearing  and  the  visceral  region  having  a  more  advanced 
contour.  The  pronephros  is  conspicuous.  The  pectoral  fin  is  present  as  a  longitud- 
inal dermal  ridge.  The  tail,  judging  from  its  twisted  condition,  is  evidently  capable 
of  active  movements.  This,  however,  in  its  detailed  structure,  as  shown  in  a  trans- 
parent preparation  (plate  vm,  fig.  46")  is  still  distinctly  immature;  its  tip  retains 
a  neurenteric  canal  (nc),  and  a  postanal  gut  (pag)._  In  the  latter  the  irregularity 
at  the  point  x  is  probably  artifact.  The  present  embryo  measured  about  20  mm. 
in  length. 


78 


Fig.  78. — Transverse  section  passing   through  the  posterior  head  region  of  embryo  of  plate  VII,  fig.  42. 

At  the  right  the  section  traverses  an  auditory  vesicle  and  the  hyomandibular  evagination.     The  latter  fuses  with 

the  ectoderm,  which  here  invaginatesi  but  no  opening  has  as  yet  been  formed. 

Fig.  79.— Transverse  section  through  the  middle  of  the  trunk  region  of  the  preceding  embryo. 
df.     Ectodermal  anlage  of  dorsal  fin.  P».     Pronephros.  »J>C.      Body  cavity. 

hb.     Hyomandibular  evagination.  *»•     Subnolochordal  rod. 

A  third  embryo  of  this  stage  is  pictured  in  plate  vm,  fig.  49"  to  d.  It  measured 
about  35  mm.  in  length,  and  was  observed  living.  It  was  this  embryo  whose 
capsule  was  taken  accidentally  on  a  trawl  line  during  one  of  the  writer's  visits  at 
Pacific  Grove.  As  already  noted,  it  was  found  developing  in  a  creamy  fluid. 
When  placed  in  a  watch-glass,  its  general  position  and  color  were  as  here  repre- 
sented. It  lay  for  a  while  on  its  side,  its  diminutive  yolk-sac  extending  outward 
from  the  body  and  the  delicate  tail  region  showing  constant  undulatory  movements. 
Most  conspicuous  were  the  bright-colored  vessels  on  the  yolk-sac,  which  outlined  a 
vitelline  circulation  obviously  shark-like.  The  visceral  cavity  showed  red  through 
the  delicate  wall,  and  in  the  gill  region  there  were  prominent  bead-like  dilatations, 
brilliant  in  color.  One  notes  the  bright  red  spot  under  the  eye,  which  was  later 


CHIMyEROID   FISHES   AND  THEIR   DEVELOPMENT. 

found  by  sections  to  represent  the  spiracle.*     Further  details  of  the  gill  region  are 
given  in  fig.  49". 

In  the  various  figures  given  of  this  embryo  we  note  a  number  of  advancing 
structures : 

(1)  The  eyes  are  now  well  formed,  protrude  widely  from  the  head,  and  are 
provided  with  a  conspicuous  lens. 

(2)  The    region   of   the   snout  shows  distinct   modeling.     Olfactory    pits   are 
present  and  are  separate  from  the  rim  of  the  mouth.     The  snout  region,  it  will  be 
seen  by  reviewing  the  preceding  figures,  notably  plate  vn,  figs.  44-46,  does  not  cor- 
respond to  the  greatly  dilated  eminence  which  forms  the  cap-like  knob  surmounting 
the  head.     This  appears  rather  in  the  region  of  the  forebrain,  and  the  writer  does 
not,  therefore,  agree  in  the  conclusions  of  Schauinsland  (who,  however,  it  will  be 
borne  in  mind,  examined  Callorhynchus,  not  Chimaera)  as  to  the  fate  of  this  singular 
organ.      It  has,  we  suggest,  the  function  of  providing  for  the  growth  of  the  contour 
of  the  antero-dorsal  head  regionf  rather  than  for  the  framework  of  the  snout,  as 
Schauinsland  suggests. 

(3)  The  mouth  has  broken  through,  and  its  margins  are  thickened.     It  shows 
distinct  movements,  although  at  irregular  intervals,  in  the  living  young.     Between 
the  rim  of  the  upper  jaw  and  the  eye  appears  the  spiracle,  and  in  a  remarkably 
anterior  position  contrasted  with  that  of  an  elasmobranch. 

(4)  The  five  gill-arches  (plate  vm,  fig.  49d)  show  well-developed  lamellae  on 
their  anterior  margins,  and  from  these  are  produced  the  external  gills.     The  latter 
extend  outward  on  either  side  to  a  distance  equal  to  about  the  diameter  of  the  head 
between  the  eyes.    The  presence  of  dilated  spaces,  blood-filled,  in  the  external  gills 
has  already  been  recorded.     It  is  worthy  of  note,  perhaps,  that  when  the  present 
specimen  was  preserved  masses  of  yolk  (plate  vm,  fig.  49b)  were  found  adhering 
to  the  gill-filaments,  a  fact  which  may  have  some  significance,  since  the  blood- 
dilated  spaces  appeared  at  points  adjacent  to  the  attached  yolk  masses.     In  this 
stage,  it  may  be  added,  the  fifth  gill-slit  has  not  as  yet  broken  through. 

(5)  The  fins  are  well  established.     The  lobe  of  the  anterior  dorsal  fin,  however, 
shows  as  yet  no  trace  of  a  spine.     The  paired  fins  are  distinct  lateral  folds,  much 
as  in  the  young  shark;  in  fact,  the  pectorals  are  even  precociously  large.     It  may  be 
added    that  the   metameral   elements  of  the   fins  were  conspicuous  in  the  living 
embryo,  since  blood-vessels  were  present  and  appeared  in  a  series  of  brilliant  spots. 
The  ventral  fins  are  drawn  together  immediately  behind  the  anus,  and  no  trace 
appears  of  a  clasping  organ  or  of  a  third  pair  of  limbs.  %     The  general  arrangement 
of  the  fins  is  best  seen  in  plate  vm,  fig.  49. 

(6)  The   yolk-sac,   in   spite   of   its  small  size,   was   perfect.     Its  structure  is 
delicate,  for  at  first  its  contour  was  smooth,  but  after  the  embryo  had  been  kept 
living  for  several  hours  in  sea-water,  it  was  noticed  that  the  surface  of   the  sac 

•This  is  not  in  the  position  in  which  Solger  (Morph.  JB.,  1876,  pp.  219-221)  expected  it  to  appear,  i.  e.,  behind  the 
articulation  of  the  mandible. 

fPossibly  as  a  larval  organ  to  protect  the  head  when  in  contact  with  the  wall  of  the  egg-capsule. 

\Cf.  T.  J.  Parker,  Nature,  vol.  xxxix,  p.  625.  With  regard  to  the  non-appearance  of  mixipterygia,  which 
certainly  occur  early  in  Chimseroid  ontogeny  (cf.  infra,  plate  ix,  fig.  50^  also  text),  it  is  possible,  of  course,  that  the 
present  embryo  was  a  female. 


DETAILS   OF   LATER    EMBRYO. 


105 


loosened  at  several  points,  giving  the  wavy  contour  noted  in  the  figure  of  the 
entire  embryo.  The  arrangement  of  the  vessels  is  clearly  shown,  and  one  traces 
the  posterior  umbilical  veins  and  the  anterior  vitelline  arteries.  At  first  sight  the 
yolk-sac  seemed  to  be  attached  anteriorly  throughout  the  length  of  the  heart  region. 
Later  examination,  however,  showed  that  a  single  stalk,  albeit  a  very  short  one, 
connected  the  sac  with  the  trunk  in  a  fashion  very  much  as  in  the  young  shark. 
(Cf.  plate  vni,  fig.  49b). 

(7)  The  lateral  line  sys- 
tem of  organs  is  already 
established.  At  either  side 
of  the  eye  sensory  pits  are 
present  and  the  backward 

growth    of    the   lateral    line  /jj&L,  /    9/      0 

,  ,  ,  j        c  .,  M&wSkffltoL          A   II   '  f^J 

could  be  traced  as  far  as  the 

anal  region. 

DETAILS  OF  THE  FOREGOING 
EMBRYO. 

In  the  sections,  figs. 
80-83,  are  shown  details  of 
the  foregoing  embryo.  In 
the  first  of  these  (fig.  80), 
in  the  eye  structures  one 
observes  the  proportionally 
enormous  size  of  the  lens. 
Particularly  noticeable, 
also,  are  the  elaborately 
branching  vessels  lying  be- 
tween the  eye  and  the  mid- 
brain  (v,  v),  a  symptom  again 
of  the  embryo's  precocious 
growth.  In  the  following 
section  (fig.  81)  the  spiracle  (s)  is  seen  to  be  continuous.  Sections  through  an 
external  gill-filament  show,  even  more  conspicuously  than  in  shark,  the  presence  of 
both  vein  and  artery  (a,  v).  In  the  same  section  we  observe  one  of  the  blood-filled 
dilatations  (d\  which  have  already  been  commented  upon.  This  appears  at  or  near 
the  end  of  the  gill-filament. 

In  fig.  82,  a  section  through  the  pelvic  region  just  anterior  to  the  anus,  we 
observe  on  the  right  side  the  opening  of  a  segmental  duct  at  sd.  Beside  it,  at  mt, 
appears  a  mesonephric  tubule.  On  the  opposite  side  of  the  body  a  corresponding 
tubule,  ;///,  opens  directly  into  the  body  cavity.  One  observes  in  the  same  section 
a  dilated  caudal  vein  at  cv,  and  above  it  the  caudal  artery.  In  the  section,  fig.  83, 
we  observe  that  the  unpaired  fins  are  already  well  established  and  that  they  are 
made  up  largely  of  mesoblast.  The  caudal  vein  and  artery  appear  as  before,  and 
the  section  traverses  numerous  muscle  plates. 


Fig.  80. — Transverse  section  through  the  eye  region  of  the  embryo  shown  in 

plate  VIII,  fig.  49. 
V,  V,  Branches  of  anterior  internal  carotid. 


io6 


CHIM^EROID   FISHES  AND  THEIR  DEVELOPMENT. 


The  latest  embryo  in  the  writer's  material,  one  of  the  specimens  secured  by 
Professor  Wilbur,  measured  5 1  mm.  in  length.  Its  age  was  said  to  be  six  months. 
(Plate  ix,  figs.  50  and  50°  to  g.)  It  is  decidedly  like  the  adult  Chimaera,  as  can  be 
seen  from  the  figures;  it  has  well-established  snout  (in  which  sensory  grooves  and 

pits  appear),  paired  and 
unpaired  fins,  and 
clasping  organs,  show- 
ing that  the  present 
specimen  was  a  male. 
On  the  other  hand,  two 
prominent  embryonic 
characters  still  appear, 
viz,  the  yolk-sac  (which 
in  the  present  specimen 
is  preserved  only  in 
part)  and  the  external 
gills,  a  tuft  of  which  is 
seen  protruding  from 
below  the  opercular 
folds.  The  external 
gills  are  shown  in  plate 
ix,  fig.  50",  c,  e,  and  e. 
Their  degree  of  differ- 
entiation is  indicated  in 
fig.  5og,  in  which  we 
note  that  in  each  fila- 
ment one  of  the  compo- 
nent vessels  is  less  con- 
Fig.  81— Transverse  section  passing  through  the  otic  vesicles  of  preceding  embryo.  At  the  torted  than  its  neigh- 
sides  external  gills  are  shown.  bor,  the  filament  thus 
a,  artery ;d,  dilated  blood  knot  in  external  gill;  ..  -piracle ;  «,  vein.  presenting  a  Ctinkly 

appearance  when  viewed  under  a  low  power.  Occasionally  a  terminal  dilatation 
is  seen.  It  will  be  noted  that  some  of  the  filaments  attain  great  length,  although 
in  general  they  are  fewer  in  this  than  in  the  earlier  stage,  a  process  of  reduction 
having  set  in  at  certain  points.*  In  lateral  view  this  embryo  shows  fragments 
of  yolk  attached  to  its  side  and  to  its  paired  fins,  a  condition  probably  artifact, 
although  deserving  mention,  since  in  the  younger  stage  yolk  masses  were 
observed  attached  to  the  gills.  Before  making  the  present  sketch,  a  portion  of  the 
opercular  fold  and  the  neighboring  external  filaments  were  removed.  The  sensory 
canals  are  well  indicated;  that  of  the  lateral  line  has  now  passed  down  the  side  of 
the  body  and  has  entered  the  tail  region.  The  mandible  is  well  established.  In 
plate  ix,  fig.  50°,  we  observe  the  extent  to  which  the  opercular  folds  overlap 
the  tuft  of  external  filaments;  we  here  observe  also  that  the  frontal  clasping  organ 

*Cf.  also  Schauinsland  (op.  cit.,  Taf.  xvi). 


DETAILS   OF  LATER   EMBRYO. 


I07 


is  long,  narrow,  and  relatively  of  great  size,  suggesting  its  origin  from  an  anterior 
fin  spine,  and  interesting  in  connection  with  paleontological  data(V/i  figs.  132-137). 
In  fig.  5Od,  an  idea  is  had  of  the  extent  of  the  overgrowth  of  the  opercular  fold  on 
the  ventral  side  of  the  head,  and  here  is  shown  also  that  the  external  gill-filaments 
arise  only  from  the  anterior  wall  of  the  gill-slit,  and  that  the  external  filaments 
increase  in  length  as  they  pass  toward  the  middle  of  each  flap.  A  detail  of  the 
ventral  fin  is  shown  in  fig.  5Of.  Here  the  mixipterygium  is  but  a  further  differen- 
tiation of  the  base  of  the  ventral  fin  (cf.  plate  via,  fig._  49b),  and  the  anterior  clasping 
organ  (acl}  evidently  represents  the  fin's  anterior  segmental  elements  (radialia) 
(cf.  also  fig.  1 1 2).  The  mouth  region 

in  this  stage  is  noteworthy,  since  it  Q*  -* 

shows  that  not  only  are  the  anterior  ^&™    ^^ 

and  posterior  dental  plates  (adp  and 
pdp)  present,  but  also  a  series  of  other 
eminences  which  are  best  interpreted 
as  rudimentary  dental  plates.  Similar 
structures  are  now  described  in  detail 
in  the  work  of  Schauinsland  on  Cal- 
lorhynchus (u.  infra).  The  present 
figure  also  indicates  the  early  stages 
in  the  curious  lip  cartilages  of  the 
Chimseroid.  They  arise  at  the  sides 
of  the  mouth  and  suggest  at  this 
stage  the  corresponding  structures  in 
shark.  In  view  of  the  recent  work 
of  Schauinsland  and  of  the  younger 
Fiirbringer  (Morph.  JB.,  1903,  vol. 
xxxi,  pp.  360-445),  we  recognize  with  interest  the  unpaired  element  at  the  mandib- 
ular  symphysis  which  is  held  to  represent  the  homologue  of  the  basihyal  of  the 
hyoid  arch.  (Cf.  fig.  1 1 1.)  In  commenting  further  upon  this  stage  we  note  that  in 
the  eye  the  iris  is  well  established,  and  that  in  the  umbilical  sac  the  yolk  material  is 
arranged  in  conspicuously  concentric  lamellae  (plate  ix,  fig.  5od). 

The  Skull. — The  skull  at  this  stage  may  be  compared  instructively  with  that 
of  a  late  embryo  of  Callorhynchus  figured  by  Schauinsland  in  Taf.  xvn,  figs.  124, 
125,  1 26,  op.  cit.  The  present  figs.  84  A-D  were,  like  the  figures  mentioned,  prepared 
from  wax-plate  models.  The  embryo  referred  to  by  Schauinsland  is  more  advanced 
than  the  present  one,  although  the  difference  in  age  does  not  appear  to  be  conspic- 
uous. On  the  other  hand,  the  figures  of  a  younger  Callorhynchus  shown  in 
Schauinsland's  Taf.  xvm,  figs.  130  and  131,  can  not  be  compared  satisfactorily 
with  the  present  specimen  of  Chimsera,  for  its  skull  was  evidently  far  less  mature, 
a  large  part  of  the  model  having  been  based  upon  outlines  of  procartilage.  A 
study  of  the  foregoing  figures  indicates  that  the  skull  of  Chimaera  is,  at  a  corre- 
sponding growth  period,  the  more  highly  modified;  the  orbits  are  larger,  the  snout 


Fig.  82. — Transverse  section  through  the  region  of  the  ventral  fins  of 

preceding  embryo. 

i>c,  Body  cavity;  crt,  caudal  artery;  cv,  caudal  vein;  nit,  tubule  of  meso- 
nephros ;  8(1,  posterior  portion  of  segmental  ducL 

Fig.  83. — Transverse  section  through  the  tail  region  of  the  preceding 
embryo. 


io8 


CHIM^ROID    FISHES    AND    THEIR  DEVELOPMENT. 


region  is  wider  and  more  compressed,  the  palato-quadrate  is  reduced  and  trans- 
ferred to  a  more  anterior  position,  nor  is  it  as  distinct  an  element  as  Schauinsland 
figures  it  in  the  kindred  genus.  As  further  evidence  of  the  more  modified  character 
ol  the  skull  of  Chimsera,  we  observe  that  the  preorbital  ridges  are  curiously 
flattened,  forming  together  a  transverse  brow-plate  in  the  young  skull;  and  that  the 


A 


Figs.  84  A-D. — Reconstruction  of  skull  of  CKim&era  embryo  shown  in  plate  IX,  fig.  50.     The  model  is  shown  in  lateral,  three-quarters 

dorsal,  and  caudal  aspects. 

Ot-6,  Anterior  and  posterior  points  at  which  the  palato-quadrate  element  has  fused  with  the  cranium  ;  etc,  roof  of  auditory  capsule  :  ch,  ceratohyal ;  /".  fora- 
men through  which  the  ophthalmic  nerve  passes  out  of  the  cranium  ;  fos,  foramen  through  which  passes  the  superficial  branch  of  the  ophthalmic  nerve; 
gh,  basihyal ;  hch,  hypochordal  portion  of  the  basis  cranii ;  /»?«,  hyomandibular :  pb,  pharyngobranchial ;  p<lf,  palato-quadrale  fissure;  pro, 
preorbital  process;  pto,  poslorbital  process;  r,  median  rostral  cartilage;  s,  spiracular  cleft  later  retained  as  the  foramen  through  which  the  hyomandibular 
branch  of  the  seventh  nerve  passes  to  ihe  under  side  of  the  skull ;  V^-  VII,  foramen  for  fifth  and  seventh  nerves. 

postorbital  ridges  are  reduced  in  size.  We  note  also  the  greater  width  of  the 
cranium  in  Chimaera  and  the  lesser  development  of  cartilage  in  the  region  between 
the  orbits.  In  short,  we  can  justly  conclude  that  at  corresponding  stages  the  skull 
of  Callorhynchus  more  closely  resembles  that  of  a  young  shark  than  does  the  skull 
of  a  young  Chimaera.  The  proportions  in  the  case  of  Callorhynchus  are  distinctly 


DETAILS   OF   LATER   EMBRYO.  109 

shark-like,  so  also  are  its  early  rostral  cartilages.  In  Chimaera,  on  the  other  hand, 
the  developmental  processes,  evidently  abbreviated,  produce  larger  orbits,  larger 
auditory  organs  (from  this  is  due  the  broadening  of  the  skull  noted  above),  coales- 
cence of  foramina,  and  altogether  a  more  mature  modeling  of  the  head.*  In  this 
form,  moreover,  we  find  in  the  hyoid  arch  more  perfectly  developed  ceratohyal  and 
greatly  reduced  pharyngobranchial  elements.  It  follows,  I  conclude,  in  view  of 
these  and  other  evident  specializations^  that  one  can  not  reverse  the  order  of 
comparison  and  regard  Chimaera  as  resembling  the" more  closely  the  ancestral  type 
from  which  in  turn  Callorhynchus  and  sharks  developed. 

COMPARISONS  WITH  OTHER  CHIM/EROIDS. 

Before  concluding  the  account  of  the  later  embryonic  stages  of  Chimssroid, 
which  we  have  hitherto  based  upon  C.  colliei,  reference  should  be  made  to  the 
conditions  known  in  other  genera  and  species. 

In  Callorhynchus. — Schauinsland  has  already  given  many  observations  upon 
the  young  of  Callorhynchus.  It  appears  from  his  figures  that  there  are  little 
outward  differences  in  the  development  of  stages  corresponding  to  those  of  plate 
vii,  fig.  45,  of  Chimara  colliei,  and  that  of  Callorhynchus  in  Schauinsland's  Taf. 
xin,  fig.  105.  Also  there  are  but  minor  differences  between  the  present  plate  vii, 
fig.  42,  and  Schauinsland's  Taf.  xm,  fig.  98.  We  may  thus  compare  also  the 
present  plate  vn,  fig.  45,  with  Taf.  xiv,  fig.  107,  also  plate  vn,  fig.  43*,  with  Taf. 
xiv,  fig.  106.  In  a  later  stage,  contrasting  Chimaera  in  plate  vin,  fig.  49,  with 
Schauinsland's  Taf.  xv,  figs.  116  and  117,  we  can  not  fail  to  note  the  more  shark- 
like  conditions  in  the  Australian  species,  and  this  is  even  more  evident  if  we  contrast 
the  still  later  stage  of  C.  colliei  given  in  the  present  plate  ix,  fig.  50,  with  Schau- 
insland's Taf.  xv,  fig.  121.  Observe  in  this  connection  the  less  tapering  tail  of 
Callorhynchus,  a  more  distinct  second  dorsal  fin  and  the  early  appearance  of  the 
row  of  dorsal  scales  which  suggest  closely  the  conditions  shown  in  Scyllium  by  Paul 
Meyer. 

In  referring  to  the  latest  embryonic  stages  in  Callorhynchus,  outline  drawings 
may  be  given  of  specimens  preserved  in  the  department  of  ichthyology  in  the 
British  Museum,  figs.  86-88,  and  in  the  Copenhagen  Museum,  fig.  89.  %  And  these 
may  in  turn  be  compared  with  the  outline  of  the  young  Callorhynchus,  fig.  85, 
figured  by  Parker  and  Haswell  in  their  Text-book  of  Zoology.  An  examination  of 
these  figures  shows  that  the  absorption  of  the  yolk-sac  takes  place,  as  one  would 
expect,  while  the  embryo  is  still  inclosed  within  the  capsule.  In  fig.  85  the  yolk- 
sac  is  of  irregular  shape,  rather  large,  and  the  embryo  still  retains  its  external  gills. 
In  figure  86  the  sac,  still  large,  is  somewhat  bilobed,  a  condition  which  becomes 


*Cf.  also  in  this  connection  the  more  advanced  condition  of  the  mixipterygia  in  Chimaera  (plate  ix,  fig.  sof,  and 
Schauinsland's  Taf.  xvi,  fig.  120). 

fin  morphological  regards  cf.  the  reduction  of  dermal  defenses,  great  size  of  head,  reduction  of  caudal  region,  differ- 
entiation of  dorsal  fin,  specialization  of  clasping  organs,  modification  of  brain. 

JFor  the  privilege  of  examining  these  valuable  specimens  the  writer  is  indebted  to  Mr.  Boulenger  and  to 
Dr.  Winge. 


no 


CHIM^ROID   FISHES  AND  THEIR   DEVELOPMENT. 


Figs.  85-89. — Latest  stages  in  the  development  of  Callorhynchus  within  the  capsule.     Nearly  actual  size. 

85.  Callorhynchus  "  antarcticus."     Detail  of  figure  given  by  Parker  and  Haswell. 

86.  Callorhynchus  sp.     Stage  in  which  the  yolk-sac  is  reduced  in  size. 

A.  Outline  of  dorsal  fin  when  unfolded .     B,  Detail  of  frontal  clasping  organ  with  surrounding  row  of  dermal  denticles. 
87  and  88.  Callorhynchus  sp.     Late  stages  in  absorption   of  yolk-sac.      The  foregoing  three  figures  are  after  specimens  in  the 

British  Museum.     (Cf.  p.  34.) 
89.  Callorhynchus  "  antarcticus,"  showing  very  late  stage  in  the  absorption  of  the  yolk-sac.      After  sketch  of  specimen  from  New 

Brighton,  New  Zealand,  preserved  in  the  Zoological  Museum  at  Copenhagen. 


"LARVAE"  OF  CHIMERA.  m 

intensified  in  the  later  stage,  fig.  87.  In  fig.  88  the  sac  is  still  irregularly  bilobed 
and  in  figure  89,  where  it  has  been  almost  completely  taken  into  the  embryo, 
the  anterior  lobe  is  still  present.  Observe  in  connection  with  these  figures  that  the 
shape  of  the  sac  is  obviously  correlated  with  the  shape  of  the  embryo  inclosed 
within  the  capsule.*  A  further  consideration  of  these  figures  leads  us  to  conclude 
that  in  the  latest  stages  of  development  the  embryo  of  Callorhynchus  rests  on  its 
side,  and  in  this  position  the  dorsal  fin  is  observed  to  lie  neatly  tucked  against  the 
side  of  the  body,  the  dermal  web  of  the  fin  being  folded  under  the  depressed  spine. 
So  also  the  paired  and  unpaired  fins  are  closely  apposed  to  the  sides  of  the  body,  the 
continuous  dorsal  and  anal  fins  folding  closely  around  the  side.  The  dorsal  fin  folds 
over  the  trunk  towards  the  left  side  of  the  embryo.  An  outline  of  its  margin, 
slightly  raised,  is  shown  in  fig.  86  A.  In  this  stage  the  appearance  of  the  frontal 
clasping  spine  is  indicated  in  fig.  86  B.  This  corresponds  obviously  to  the  con- 
dition which  is  figured  in  a  younger  stage  by  Schauinsland  in  his  Taf.  xvi,  fig.  122. 
In  Chimcera. — The  only  late  embryonic  stage  known  to  the  writer  is  the  one 
preserved  in  the  Jardin  des  Plantes  and  figured  by  Professor  Vaillant  in  his 
"  Travailleur "  report  (1882),  a  specimen  which  the  writer  had  the  opportunity  of 
examining  through  the  courtesy  of  its  describer.  This  specimen  (fig.  90  A,  B), 
probably  of  C.  affinis,  was  dredged  in  the  Bay  of  Biscay,  together  with  fragments  of 
its  egg-capsule.  A  small  yolk-sac  is  adherent;  this  is  of  spherical  form,  and  appears 
to  have  been  delicately  connected  with  the  body  of  the  embryo.  It  is  possible, 
of  course,  that  the  present  spherical  form  of  the  yolk-sac  may  have  been  the  result 
of  the  specimen  having  been  freed  from  the  capsule,  for  under  this  condition  the 
yolk-sac  would  probably  have  assumed  its  present  shape.  It  may  be  noted  that 
the  surface  of  the  sac  was  deeply  creased  with  blood-vessels,  somewhat  as  indicated 
in  fig.  90  A.  Noteworthy  in  this  specimen  is  the  great  length  of  the  hinder  trunk 
(and  tail)  which,  it  will  be  seen,  is  proportionately  longer  than  in  Chimara  colliei, 
and  much  longer  than  in  Callorhynchus,  and  it  is  also  to  be  mentioned  that  the 
long  urostyle  shows  that  the  continuous  dorsal  fin  could  not  have  extended  function- 
ally into  this  posterior  region.  Clasping  organs  are  developed,  and,  as  shown  in 
fig.  90  B,  they  attain  even  now  a  considerable  size,  about  one-third  their  adult 
(proportional)  length.  This  condition  is  noteworthy  as  indicating  again  a  precocious 
type  of  development,  sexual  characters  having  been  differentiated,  although  the 
embryo  is  small  in  size  and  provided  with  a  considerable  yolk-sac. 

IMMATURE  YOUNG. 

Four  stages  of  "larvae"  of  Chimcsra  colliei  are  shown  in  plates  x  and  xi,  to 
illustrate  especially  changes  in  outward  form,  proportions,  and  coloration.  The 
specimens  figured  in  plate  x  were  secured  by  the  Albatross  during  its  work  on  the 
Pacific  coast,  and  were  kindly  placed  at  the  writer's  disposal  by  the  United  States 
National  Museum.  The  youngest  specimen  figured  (fig.  51  and  figs.  51*  and  b) 
was  evidently  lately  hatched.  It  still  shows  the  scar  marking  the  point  of  intrusion 

*The  irregular  outline  of  the  yolk-sac  would,  by  analogy,  probably  be  filled  out  if  the  living  embryo  were  removed 
from  the  constricting  capsule. 


I  12 


CHIM^EROID    FISHES    AND    THEIR   DEVELOPMENT. 


of  the  yolk-sac  (plate  x,  fig.  5ib,  ys);  its  form  at  this  stage  is  probably  modeled 
somewhat  differently  from  that  of  the  latest  stage  of  the  encapsuled  embryo;  thus 
the  membranes  of  the  unpaired  fin  in  the  tail  region  are  probably  less  marked  than 
in  the  earlier  stage  (comparing  the  embryo  of  plate  ix,  fig.  50)  in  which  this  mem- 
brane serves  as  an  organ  for  carrying  out  the  water  used  in  the  respiration  of  the 

go 


Fig.  90. — Late  stage  of  Chimrera  affinis  (>). 

The  yolk-sac  is  largely  resorbed.     The  present  is  the  type  specimen  of  Professor  VailUnl,  and  i>  preserved  in  the  ichthyological  museum  of  the  Jardin 
des  Plantes,  bearing  the  number  42392.     In  spite  of  its  small  size  (its  total  length  is  only  about  1  I   cm.)  it  shows  a  well-developed  mixipterygium 
(B) .     A  detail  showing  the  vascular  supply  of  the  yolk-sac  is  indicated  at  A. 
Fig.  91. —  Detail  of  early  Chimeera  monstrosa,  showing  larval  coloration. 

After  sketch  of  specimen  in  the  museum  of  Tromsoe.     Colors  are  indicated,  a,  ashen,  if,  white. 
Fig.  92.— Detail  of  Chimsera  monstrosa  indicating  final  larval  coloration.     After  sketch  of  specimen  in  the  museum  in  Copenhagen. 

encapsuled  young.     The  advancing  characters  of  the  earlier  young  may  best  be 
followed  by  contrasting  figs.  51,  52,  and  53.     The  changes  thus  observed  are: 

In  proportions. — The  head  length  of  the  embryo,  measured  for  example  anterior 
to  the  base  of  the  dorsal  fin,  decreases  as  we  ascend  the  scale ;  in  the  earlier  stage  it 
measures  about  20  per  cent,  of  the  entire  length,  in  the  latest  about  16  per  cent. ; 
the  eye  alters  little  in  size,  but  the  region  of  the  head  lying  below  the  eye  increases 
notably;  the  shape  of  the  pectoral  fin  changes  progressively;  almost  as  wide  as  high 
in  the  first  figure,  it  becomes  nearly  twice  as  high  as  wide  in  the  latest  stage.  So, 


"LARV.E"  OF  CHIMERA.  113 

too,  the  unpaired  fins  change  proportions  notably;  in  the  stage  shown  in  plate  x, 
fig.  52,  their  width  is  much  greater  proportionately  than  at  other  stages. 

In  shape. — The  shape  of  the  trunk  undergoes  noteworthy  changes.  In  the 
stage  shown  in  plate  x,  fig.  53,  it  is  much  longer  proportionately  than  in  the  earlier 
and  later  stages.  We  note  also  that  the  dorsal  fin  (or  rather  that  portion  of  it 
posterior  to  the  first  dorsal)  changes  from  continuous  to  lobate  and  then  again  later 
to  a  lower  and  less  lobate  form,  during  progressive  development. 

In  color. — Pigmentation  appears  progressively.  In  the  youngest  stage  the  pig- 
mented  areas  are  dorsal.  In  the  stage  of  plate  x,  fig.  53,  pigmentation  is  more 
marked  on  the  sides  of  the  body  than  at  any  other  stage.  The  sharpness  in  the 
coloration  of  the  distal  margin  of  the  dorsal  fins  is  most  conspicuous  in  the  stage  of 
plate  x,  fig.  52;  also  a  distinct  larval  coloration  is  noticed  in  the  pectoral  fin,  a  well- 
marked  color  being  present  along  the  anterior  margin  of  this  fin  and  in  the  anterior 
portion  of  its  dermal  web.  Observe  also  the  distinct  patch  of  pigment  at  the  base 
of  the  dermal  web  in  plate  x,  fig.  53.  Noteworthy,  further,  is  the  progressive 
increase  in  the  number  of  pigmentless  blotches;  few  in  fig.  51",  they  become 
numerous  in  fig.  53",  and  small  and  most  numerous  in  the  stage  of  plate  x,  fig.  54. 
Similar  changes  in  coloration  affect  the  region  of  the  eye. 

A  late  stage  in  the  development  of  Chimcera  colliei  may  finally  be  referred  to  in 
plate  XT.  At  this  age  the  young  fish  has  attained  nearly  mature  size  (i.  e.,  about 
three-quarters  of  that  of  the  adult),  although  it  is  still  distinctly  "larval."  Its 
coloration  is  darker  (cf.  fig.  i),  making  the  small  pigmentless  spots  more  con- 
spicuous. The  margins  of  the  fins,  on  the  other  hand,  are  pigmented,  and  with 
these  we  may  contrast  the  fin  margins  in  the  adult,  figs,  i  and  2,  especially  in  the 
latter  figure,  where  we  observe  that  the  anterior  rim  of  the  paired  fins,  notably  the 
ventral,  are  pigmentless.  We  observe  also  distinct  changes  in  proportions  from 
the  earlier  stages;  the  length  of  the  fish  anterior  to  the  anal  region  is  now  scarcely 
more  than  one-half  the  total  length;  in  the  earlier  stage  figured  it  is  less  than  one- 
third.  In  the  present  specimen,  a  young  male,  the  ventral  fins  partly  uncover  the 
mixipterygia ;  the  ventrals  are  small  in  size,  surprisingly  so  when  we  consider  the 
length  of  the  entire  fish.  At  this  growth  period  the  young  of  this  species  occur  in 
schools  and  sometimes  appear  in  shallow  water.  * 

In  other  species  similar  changes  in  colors  and  proportions  are  probably  present 
in  "larval"  young.  In  one  species,  Chimcera  monstrosa,  they  are  present  in  even 
a  more  marked  condition.  In  a  young  specimen  preserved  in  the  museum  of 
Tromsoe,  to  which  the  writer's  attention  was  kindly  called  by  Dr.  V.  Storm,  the 
coloration  was  brilliantly  marked.  Although  not  larger  than  the  specimen  shown 
in  plate  x,  fig.  53,  it  had  developed  dorsals  sharply  marked  with  black,  pectorals 
with  an  ashen  blotch  and  with  a  white  anterior  rim,  a  pattern  which  has  been 
reproduced  from  a  sketch  in  the  present  fig.  91.  It  is  evident,  moreover,  that 
in  C.  monstrosa  this  stage  is  of  brief  duration;  for  in  a  second  and  equally  well- 

*The  present  specimen  was  taken,  together  with  22  others,  in  a  water  depth  of  less  than  10  feet,  near  Port  Wash- 
ington, Puget  Sound,  June,  1896,  in  a  single  haul  of  a  herring  seine.  In  this  locality  Chimaera  is  rarely  taken  in 
shallow  seines.  The  specimens  measured  from  30  to  40  cm. 


H4  CHIM^ROID    FISHES    AND    THEIR  DEVELOPMENT. 

preserved  specimen  of  this  species — one  which  was  examined  in  the  Copenhagen 
collection — the  colors  had  notably  changed.  The  pigmented  margins  of  caudal 
and  postdorsal  fins  had  become  reduced  to  a  dusky  band,  and  the  marking  of  the 
pectoral  was  limited  to  a  mere  fuscous  blotch  at  the  fin  tip  (fig.  92).  The  length  of 
this  specimen  was  but  about  two  inches  greater  than  the  former  one. 

From  the  foregoing  notes  we  may  justly  conclude  that  Chimaera  undergoes 
a  series  of  "larval"  changes.  That  these  are  adaptive  remains  still  to  be  proven, 
a  verdict  which,  it  may  be  remarked,  applies  equally  well  to  many  if  not  all  the 
"larval  "  changes  of  teleosts,  but  the  fact  that  such  changes  do  occur  in  the  hatched 
young  is  noteworthy  in  its  bearing  on  the  specialized  nature  of  Chimaeroid 
development.  It  is  also,  I  believe,  significant  that  the  "larval  "  coloration  of  the 
young  of  Chimtzra  monstrosa  occurs  at  an  earlier  relative  period  than  in  C.  colliei 
(i.  e.,  that  the  distinctness  of  coloration,  which  in  C.  colliei — a  smaller  species  by  the 
way — is  shown  in  a  specimen  twelve  inches  in  length,  is  attained  in  monstrosa  by 
the  time  the  young  measures  but  about  seven  inches),  for  this  denotes  that  the 
structures  of  monstrosa  are  the  more  highly  differentiated  and  that  this  species  is 
of  later  origin.  In  another  direction  it  contributes  testimony  as  to  the  abbrevia- 
tion of  developmental  processes. 

ORGANOGENY. 
INTEGUMENT  AND  DENTITION. 

In  the  major  problem  of  the  position  of  Chimaeroids  the  evidence  of  scales  and 
dentition  claims  an  important  place.  For  the  question  has  been  raised  repeatedly 
whether  the  dentition  of  these  fishes  is  fundamentally  different  from  that  of  sharks, 
and  whether  the  characteristic  tritoral  plates  may  not  have  retained  primitive  gnath- 
ostomal  characters  (Jaekel).  And  it  has  similarly  been  queried  (Pollard)  whether 
the  present  integumental  defenses  of  Chimaeroids  may  not  prove  the  rudiments  of 
a  complete  body  armoring.  We  may  accordingly  review  at  this  point  the  evidence 
in  the  matter  of  integument  and  teeth  afforded  by  a  study  of  the  recent  forms,  both 
in  adult  and  in  embryonic  condition. 

It  has  long  been  known  that  recent  Chimaeroids  retain  shagreen-like  structures. 
These  occur  in  greater  or  less  number  (a)  on  either  side  of  the  median  dorsal  line ; 
(<$)  in  connection  with  sensory  canals,  especially  in  the  suborbital  region;  and  (c)  in 
the  male  as  organs  of  retention  in  copulo. 

(a)  Shagreen-like  scales  on  either  side  of  the  median  line  are  most  numerous  in 
Callorhynchus,  where  they  form  rows,  each  including  about  a  dozen  scales,  in  three 
definite  tracts,  i.  e.,  in  the  head,  between  the  first  and  second  dorsals,  and  between 
the  second  dorsal  and  the  caudal  fin  (figs.  93  A  and  B).  In  Harriotta  they  are 
smaller  and  less  numerous.  In  Rhinochimaera  they  are  tumid  and  uncalcified, 
occurring  along  the  fleshy  anterior  margin  of  the  caudal  fin,  obsolescent  elsewhere. 
In  Chimaera  they  are  rudimentary  or  absent.  These  scales  occur,  therefore,  in  a 
regressive  series,  at  one  end  of  which  stands  Callorhynchus,  at  the  other  Chimaera; 
and  it  is  significant,  I  believe,  that  a  condition  closely  similar  to  Callorhynchus 
occurs  in  sharks,  e.  g.,  Pristiurus  and  Scyllium,  as  figured  by  Paul  Meyer,  who, 


SHARK-LIKE  DERMAL  DENTICLES. 


D 


E 


Figs.  93  A-F. — Dermal  denticles  of  Callorhynchus. 


The  dorsal 


A.  Dona!  aspect  of  young  Callorhynchus  "  antarcticus"  (Chili),  measuring  16  cm.  in  length. 

denticles  are  conspicuous ;  their  disposition  and  number  is  indicated. 

B.  Dorsal    aspect  of  well-grown   Callorhynchus  "antarcricus"   (Chili),   measuring  50  cm.  in  length.    The 

dorsal  denticles  are  reduced.     In  a  specimen  (Australian)  measuring  92  cm.  they  do  not  appear. 

C.  Isolated  denticle  from  the  back  of  a  late  "  embryo."     X  42.     After  Schauinsland. 

D.  Isolated  denticle  of  a  late  "embryo"  (shown  from  side).     X  42.     After  Schauinsland. 

E.  Row  of  four  denticles  from  the  back  (in  front  of  second  dorsal  fin)  of  a  late  "embryo."    After  Schauinsland. 

F.  Enlarged  denticle  from  similar  situation  in  "  adult "  specimen.     X  21.    After  Schauinsland. 


ng  CHIMyEROID   FISHES  AND  THEIR   DEVELOPMENT. 

however,  does  not  refer  to  these  structures  in  connection  with  Chimsera  (MT.  Zool. 
Stat.  Neapel,  vi,  p.  221  et  seq.\  In  further  detail:  in  the  dorsal  scales  of  Callo- 
rhynchus,  as  Dumeril  and  others  have  shown,  the  individual  scales  are  furcate  at 
their  base,  and  the  free  points  of  the  base  project  forward  and  embrace  the  pre- 
ceding member  of  the  series,  thus  rendering  the  row  of  scales  stronger  and  more 
compact  (cf.  esp.  Dumeril,  Carman,  and  Schauinsland).  (Figs.  93  C-E.)  It  has 
further  been  shown  by  Schauinsland  that  these  scales  present  notable  shark-like 
features  in  their  development;  they  first  arise,  like  shagreen  denticles,  as  an  out- 
growth of  the  derma;  they  then  differentiate  odontoblasts,  by  which  in  a  centrifugal 
direction  dentine  is  laid  down ;  and  at  the  end  of  the  process  a  pulp  cavity  remains 
and  a  basal  plate  perforated  by  small  nutrient  canals.  In  Schauinsland's  words  we 
further  note  that  "in  the  latest  embryonal  stages  the  denticles,  and  especially  their 
tips,  acquire  a  greater  and  glassy  transparency  (vitrodentine),  by  which  they 
become  more  and  more  differentiated  from  the  substance  of  the  (basal)  plate.  In 
short,  developmentally  speaking,  the  dermal  denticles  of  Callorhynchus  represent 
the  most  primitive  scales  which  occur  among  living  selachians.  Through  the 
presence  of  a  basal  plate  perforated  by  dentine  tubules,  they  suggest  the  scales  of 
the  oldest  palaeozoic  selachians. "  *  Schauinsland  illustrates  his  foregoing  remarks 
with  two  excellent  figures,  one  showing  in  section  an  early  stage  (pp.  cit.,  Taf.  xix, 
fig.  139)  in  the  development  of  the  dermal  cusp,  the  other  a  late  stage  in  which 
the  cusp  presents  a  thick  cortical  layer  of  vasodentine  (ibid.,  fig.  140),  projecting 
its  tip  beyond  the  epidermis. 

On  the  basis  of  the  foregoing  observations,  therefore,  we  may  conclude  that,  as 
far  as  these  body  scales  are  concerned,  Callorhynchus  is  distinctly  shark-like;  there 
is  not  the  slightest  embryological  evidence  that  this  Chimaeroid  had  ever  ganoid- 
like  scales.  We  might  even,  I  think,  go  farther  than  Schauinsland,  and  point  out 
resemblance  with  more  typical  selachian  conditions;  for  this  author,  while  main- 
taining that  "the  epidermis  takes  no  part  in  the  formation  of  the  denticle,"  and 
admitting  that  he  "was  unable  to  demonstrate  the  presence  of  enamel,"  shows 
nevertheless  in  his  earlier  figure  that  the  cells  of  the  epidermis  are  arranged  over 
the  dermal  papilla  in  a  wayf  that  is  more  than  suggestive  of  an  enamel  organ— 
an  emphatically  shark-like  character;  and  we  may  further  conclude  that  the  base 
of  the  denticle  perforated  with  tubules  is  not  merely  characteristic  of  denticles  of 
Silurian  forms  but  of  later  sharks  as  well  (cf.  Rose,  re  trabeculo-dentine  in  Anat. 
Anz.,  1897,  P-  S^)-  In  connection  with  the  presence  of  scales  arranged  near  the 
dorsal  line,  it  has  already  been  commented  on  (Schauinsland)  that  these  structures 
are  relatively  more  prominent  in  the  late  embryo  than  in  the  adult,  although 
no  explanation  of  this  phenomenon  has  yet  been  advanced.  I  may  accord- 
ingly hazard  the  opinion  that  they  have  been  retained  in  this  position  owing  to 
their  importance  as  larval  organs — possibly  for  the  purpose  of  enabling  the  well- 

*Cf.  Rohon,  J.  O.,  Ober  fossile  Fische  vom  oberen  Jenissei,  Mem.  Acad.  St.  Petersburg,  1889,  and  Die  ober- 
silurischen  Fische  von  Oesel,  Mem.  Acad.  St.  Petersburg,  1893.  He  refers  to  denticles  of  Thelodus-like  forms  which 
the  recent  researches  of  Traquair  have  associated  with  fishes  which  are  in  some  regards  shark-like. 

\Cf.  e.g.,  Jentsch,  B.,  Beitr.  z.  Entwick.  u.  Struktur  d.  Selachierzahne.     Leip.  1897,  fy?-  6. 


SHARK-LIKE  DERMAL  DENTICLES.  117 

developed  young  to  maintain  its  position  in  the  egg-capsule,  possibly  also  for  the 
purpose  of  protecting  the  delicate  dorsal  fin,  i.  e. ,  by  keeping  it  from  rubbing  against 
the  walls  and  the  roof  of  the  capsule,  during  the  movements  of  the  young  fish. 
According  to  this  view  the  dorsal  scales  of  the  young  Callorhynchus  after  the  time 
of  hatching  are  to  be  looked  upon  merely  as  rudimentary  organs.*  And  it  may 
be  pointed  out,  in  this  connection,  that  when  these  enlarged  dorsal  scales  are 
developed  in  shark  embryos  they  appear  only  in  those  forms  in  which  development 
takes  place  in  egg-capsules.^ 

(£)  Small  dermal  plates  have  long  been  known  to  occur  in  Chimseroids  in 
connection  with  the  sensory-canal  system.  Pollard  makes  a  special  reference  to 
those  situated  in  the  suborbital  canals,  and  Schauinsland  gives  the  following  notes 
upon  them  (pp.  cit. ,  p.  13): 

In  the  immediate  neighborhood  of  the  mucous  canals — I  have  investigated  those  only  situated 
on  the  head — there  also  occur  dermal  calcifications.  I  find  there  (in  transverse  section)  in  the 
floor  of  the  canal  (in  the  neighborhood  of  the  skull)  a  large  plate,  and  in  addition  at  its  sides  and 
bounding  it  four  to  six  conical  caps  of  dentine.  The  development  of  these  is  like  that  of  the 
denticles,  save  that  the  plate  contains  no  pulp  cavity,  while  the  lateral  small  hard  structures 
present  such  a  cavity,  if  indeed  only  in  a  narrow  form,  and  filled  with  few  cells,  whereby  they 
come  to  resemble  a  small  denticle.  These  calcifications  are  also  probably  only  the  rudiments  of 
former  dermal  denticles  which  came  to  sink  down  at  the  same  time  that  the  epidermis  was  invag- 
inated  to  form  the  mucous  canals ;  in  this  process  they  lost  their  primitive  form  and  underwent 
degeneration.  In  adult,  and  especially  in  a  number  of  fossil  Holocephali  the  slime  canals  are 
surrounded  by  a  great  number  of  closely  compressed  rings  formed  of  calcified  and  bony  material ; 
these  had  their  origin  through  a  process  of  pressing  together  the  single  dentine-like  bony  caps 
noted  in  the  embryo. 

In  the  matter,  then,  of  the  character  of  these  plates  in  living  forms,  we  may  again 
conclude  that  they  are  equally  derived  from  solitary  dermal  denticles,  shark-like  in 
type.  There  is  no  evidence,  on  the  side  of  embryology  at  least,  that  these  plates 
result  from  a  breaking  down  of  larger  structures.  It  is  only  necessary  to  note 
further  that  these  structures  in  Callorhynchus  are  most  marked  in  their  likeness  to 
the  selachian  condition,  and  that  they  are  least  marked  in  the  case  of  Chimaera.  \ 

(c)  In  all  recent  Chimseroids  numerous  denticles  are  present  in  the  male,  i.  e., 
on  the  frontal  clasping  organ,  on  the  mixipterygium,  and  on  the  anterior  pelvic 
clasping  organ.  These  denticles  have  a  transparent,  almost  glassy  character.  In 
the  frontal  clasping  organ  of  Callorhynchus,  they  occur  not  only  at  the  tip  of  the 
organ  itself,  but  also  proximalward  and  at  the  front  and  sides  of  the  depression  into 
which  this  clasping  organ  fits;  but  in  the  other  genera,  the  denticles  are  limited 
only  to  the  tip  of  this  organ.  It  follows,  accordingly,  that  in  Callorhynchus  appears 
again  a  more  shark-like  character,  i.  e.,  a  greater  number  of  denticles  spread  over 
a  larger  extent  both  of  the  clasping  organ  itself,  and  of  the  sheath  into  which  the 

*In  a  specimen  of  Callorhynchus  "  antarcticus"  (Australia),  measuring  92  cm.  in  length,  the  dorsal  denticles 
have  disappeared. 

fThe  tubercles  in  the  encapsuled  Scyllium  (de  Philippi,  Paul  Meyer)  may  well  have  a  similar  function.  By 
Paul  Meyer  they  are  described  (op.  cit.,  p.  224)  as  rudimentary  organs,  viz.,  the  remains  of  the  ancestral  annelidan 
parapods! 

$As  to  the  condition  of  these  dermal  elements  in  fossil  Chimaeroids,  j>.  figs.  138  and  139  ;  by  evidence  thus  obtained 
the  conclusion  becomes  definite,  i.  e.,  that  the  shagreen  of  recent  forms  has  been  greatly  reduced  from  a  condition 
altogether  shark-like. 


jjg  CHIM^ROID   FISHES  AND  THEIR  DEVELOPMENT. 

clasping  organ  is  usually  depressed.  In  this  connection  we  call  to  mind  the  great  size 
of  the  clasping  organ  in  the  young  Callorhynchus,  suggesting  its  origin  from  an 
anterior  fin  spine  (cf.  figs.  132-137);  its  small  size  in  Chimaera  on  the  other  hand 
indicates  the  later  derivation  of  this  genus. 

This  induction  is  also  supported  by  a  study  of  the  clasping  organs  connected 
with  the  ventral  fins  in  the  antero-pelvic  clasping  organ  of  Callorhynchus.  We 
observe  that  this  structure  is  furnished  with  many  dermal  denticles — 40  or  there- 
abouts in  the  case  of  Callorhynchus  antarcticus,  according  to  Dumeril,  whereas  in 
the  various  species  of  Chimsera  and  in  Rhinochimaera  the  number  is  reduced,  varying 
usually  from  about  six  to  three. 

In  the  mixipterygium  shagreen  denticles  occur  plentifully.  In  the  case  of  one 
arm  of  this  trifid  organ  in  Chimcera  colliei  the  denticles  extend  proximally  as  far  as 
the  base  of  the  organ.  In  the  other  two  arms  the  shagreen  is  limited  to  tracts 
near  the  tips.  An  abundant  supply  of  these  denticles  is,  however,  present,  repre- 
senting, in  fact,  tracts  of  shagreen.  In  Chimcera  monstrosa,  on  the  other  hand,  the 
amount  of  the  shagreen  is  less,  a  condition  which  furnishes  another  reason  for 
regarding  this  species  as  the  more  modified.  In  Rhinochimczra  pacifica,  as  the 
writer  has  already  noted  (Jour.  Sci.  Coll.  Tokyo,  vol.  xix,  p.  10),  the  shagreen  at 
the  tip  of  the  mixipterygium  is  greatly  reduced.  In  Callorhynchus,  on  the  other 
hand,  it  is  as  abundant  as  in  the  case  of  Chimara  colliei. 

.  DENTAL  PLATES. 

These  have  always  been  the  stumbling-block  in  comparing  Chimseroid  with 
sharks,  for  by  only  superficial  comparison  have  the  tritoral  areas  in  the  dental 
plates  of  Chimseroids  been  regarded  as  equivalent  to  the  teeth  or  clusters  of  teeth 
in  the  shark.  Nor  has  paleontology  as  yet  been  able  to  elucidate  the  problem, 
even  to  the  degree  in  which  it  has  thrown  light  upon  the  origin  of  the  dental  plates 
in  the  lung-fishes.  In  fact,  as  we  shall  later  note,  the  study  of  the  dentition  of 
fossil  Chima^roids  leads  us  at  the  present  time  to  no  decisive  results.  The  develop- 
ment of  the  dental  plates  might  therefore  be  looked  to  to  furnish  evidence  as  to  the 
nature  of  these  structures.  For  it  is  well  known  that  through  embryology  a  flood  of 
light  has  been  thrown  upon  the  mode  of  origin  of  the  dentition  of  lung  fishes. 
Accordingly,  we  conclude  that  one  of  the  most  important  sections  of  Schauinsland's 
memoir  on  Callorhynchus  is  devoted  to  the  question  of  the  mode  of  origin  of  the 
dental  plates. 

Schauinsland's  account,  indeed,  is  of  such  value  in  the  present  connection  that 
I  have  been  led  to  quote  it  in  freely  translated  form  (pp.  tit.,  pp.  13-16)  : 

In  even  their  earliest  stages  the  dental  plates  are  laid  down  as  distinct  elements,  i.  e.,  four 
above  and  two  below,  and  there  is  at  no  time  a  definite  indication  that  these  are  composed  of 
simpler  elements  which  have  fused  together.  The  upper  anterior  plates  are  certainly  simple ; 
the  remaining  pairs,  however,  show  along  their  hinder  (caudal)  border  a  somewhat  trifid 
arrangement.  In  this  region,  too,  the  plates  with  their  three  ridges  pass  into  a  fold  of  the  skin, 
and  here  their  growth  takes  place.  (No  trace  appears  even  in  earlier  stages  of  the  median 
(unpaired)  mandibular  tooth  which  has  been  described  in  fossil  Chimseroids.)  If  we  regard  the 
three  ridges  as  rows  of  teeth  which  have  become  fused  together,  they  would  have  obviously  a 
certain  similarity  to  the  dental  plates  of  dipnoi  or  even  of  teleosts  (e.  g.,  Anarrhichas);  and  we 


THE  ORIGIN   OF   THE   DENTAL   PLATES.  119 

might  accordingly  regard  the  anterior  plates  as  premaxillary  or  vomerine,  although  in  the  latter 
regard,  i.  e.,  re  premaxillary  and  vomerine  elements,  we  query  whether  we  can  justly  introduce 
this  comparison  in  the  holocephali.  On  the  other  hand,  if  the  comparison  be  a  legitimate  one,  we 
might  even  go  farther  and  regard  the  more  median  ridge  of  the  large  plates  of  the  mouth-roof 
as  equivalent  to  the  fused  vomerine  teeth,  and  look  upon  the  remainder  of  these  plates  as  having 
arisen  from  fusion  of  the  elements  in  a  double  row  of  palatine  teeth.  Of  course,  however,  such 
an  interpretation  would  be  purely  hypothetical. 

One  is  inclined  to  look  upon  the  anlage  of  a  dental  plate  as  the  product  of  a  single  and 
enormously  enlarged  dental  papilla,  circumscribed  by  a  dermal  fold,  the  induplicature  of  which  is 
deepest  at  the  posterior  margin  of  the  papilla.  The  first  deposition  of  hard  material  begins  at  the 
outer  surface  of  the  papilla,  and  takes  the  form  of  a  thin  cap  of  dentine,  soon,  however,  the  tooth- 
substance  appears  below  at  the  points  where  the  plate  is  to  come  in  contact  with  the  cartilage  of 
the  head.  And  almost  at  the  same  time  trabeculse  and  lamellae  appear  between,  i.  e.,  in  the 
substance  of  the  plate,  and  produce  a  rneshwork  of  spongy  tooth-substance  (pulp-dentine).  The 
mode  of  origin  of  the  plate  resembles  closely  that  of  bone  when  derived  from  connective  tissue 
(e.  g.,  in  Sphenodon).  The  mesenchyme  cells  in  the  papilla  are  collected  together  closely 
at  certain  points  and  become  transformed  into  odontoblasts,  and  from  these,  peripherally,  the 
dentine  takes  its  origin.  It  may  be  remarked  that  the  dentine  is  sometimes  laid  down  in  an 
irregular  way,  with  branching  processes,  its  canals  ramifying,  unlike  the  parallel  canals  of  true 
dentine.  Occasionally  trabecules  of  the  dental  mass,  especially  in  older  individuals,  show  a 
somewhat  lamellar  structure,  and  those  which  are  first  differentiated,  that  is,  those  lying  inner- 
most, are  distinguishable  from  the  later  lamellae  by  their  capacity  to  become  stained.  As 
already  noted,  the  entire  dental  plate  is  finally  formed  of  a  meshwork  of  dentine-like  material, 
whose  trabecules  thicken  with  age,  so  that  finally  the  plate  attains  a  high  degree  of  hardness. 
The  spaces  between  the  meshwork  represent  collectively  a  large,  greatly  branched  pulp  cavity, 
whose  cells  in  part  have  retained  their  former  reticular  arrangement,  in  part  have  become  odonto- 
blasts, as  far  at  least  as  they  become  opposed  to  the  trabecules.  In  the  various  ramifications 
of  the  pulp  cavity  blood-vessels  are  often  present.  Enamel  is  not  deposited;  nevertheless  the 
epidermis  cells  must  have  a  certain  influence  on  the  character  of  the  dentine,  since  the  dentine 
becomes  glassy  in  character  when  in  contact  with  the  epidermis,  but  remains  unchanged  when- 
ever the  epidermis  is  lacking.  The  dental  plates  are  fastened  to  the  head  cartilage  by  means  of 
a  firm  layer  of  connective  tissue,  which  indeed  here  and  there  may  enter  the  substance  of  the 
plate,  and  for  still  stronger  attachment  claw-like  outgrowths  arise  from  the  base  of  the  plate, 
especially  from  its  anterior  and  lateral  portions. 

Finally,  I  must  refer  to  the  presence  of  remarkable  structures  in  the  dental  plates,  which  occur 
only  within  the  ridges  above  referred  to.  These  take  the  form  of  a  chalky  mass,  which  appears 
in  cleared  preparations  and  can  be  traced  throughout  the  entire  length  of  a  dental  ridge  ;  it 
is  partly  inclosed  within  the  meshes  of  the  trabecules  of  the  dentine,  and  by  these  partly 
again  broken  up  into  rounded  masses  and  processes.  In  transverse  section  this  chalky  mass 
presents  the  appearance  of  a  section  of  a  many-rooted  tooth,  while  in  longitudinal  section  its 
substance  appears  continuous,  although  greatly  fenestrated.  A  more  detailed  examination 
shows  that  we  are  here  dealing  with  an  especial  variety  of  dentine;  that  is,  differentiated  from 
odontoblast-like  embryonic  cells,  whose  processes  grow  deeply  down  and  develop  canals  which 
from  their  parallel  arrangement  recall  strikingly  those  of  typical  dentine.  In  any  event,  the 
material  in  question  can  more  accurately  be  designated  as  dentine  than  can  the  remaining  spongy 
substance  of  the  dental  plate.  From  the  latter  it  is  also  distinguished  in  remaining  colorless 
after  treatment  with  the  usual  stains  for  bone,  and  especially  in  retaining  permanently,  even  in 
the  grown  Callorhynchus,  its  soft  and  uncalcified  condition.  It  may  be  noted  that  this  soft 
dentine  is  not  present  in  the  youngest  embryonic  stages  ;  it  appears  shortly  after  the  caudal  ends 
of  the  plate  are  established  and  extends  gradually  from  a  hindward  into  a  more  anterior  position. 

It  has  nothing  to  do  with  the  origin  of  the  hard  structures  of  the  plate,  since  it  appears  after 
these  have  been  laid  down.  It  usually  appears  somewhat  deeper  than  the  outer  surface  of  the 
plate  ;  later  it  often  comes  to  lie  in  close  contact  with  it,  and  even  extends  thence  inward,  not 
infrequently  coming  to  be  associated  with  the  remaining  meshwork  of  the  dentine.  What  the 
significance  of  this  structure  is  remains  in  any  event  doubtful,  and  only  with  reserve  do  I  express 
the  opinion  that  these  soft  masses  of  dentine  represent  the  rudiments  of  former  rows  of  single  or 


I2o  CHIM/EROID  FISHES  AND  THEIR  DEVELOPMENT. 

already  fused  teeth,  which  had  primitively  passed  from  behind  and  taken  up  a  position  on  the 
dental  ridges.  In  the  case  of  these  teeth  (a  similar  process  occurs  in  the  ontogeny  of  Cerato- 
dus)  spongy  dentine,  or  bone-like  masses,  were  differentiated  in  the  course  of  phylogenetic 
development,  and  these  became  finally  of  greater  value  for  purposes  of  nutrition  than  the  separate 
teeth  ;  and  they  accordingly  fused  together,  overgrew  the  teeth,  and  in  the  end  completely 
enveloped  them.  And  since  the  teeth  had  no  longer  their  primitive  function,  they  came  to  lose 
their  limy  structure  and  degenerated,  remaining  in  the  condition  in  which  we  see  them  to-day. 
While  their  arrangement  in  three  rows  possibly  indicates  an  alliance  with  the  higher  forms, 
their  mode  of  successional  growth  suggests  the  origin  of  the  rows  of  teeth  of  selachians. 

The  results  of  the  foregoing  observations  of  Schauinsland,  it  will  be  seen,  are 
disappointing  to  those  who  on  a  priori  grounds  anticipated  that  the  dental  plates 
of  Chimaeroids  would  in  the  ontogeny  of  recent  species  be  found  to  be  formed  of 
the  coalesced  bases  of  separate  tooth  elements,  which,  in  their  turn,  would  of 
course  be  homologous  with  those  of  sharks.  One  may,  nevertheless,  I  believe, 
take  a  somewhat  more  hopeful  view  of  this  problem,  in  view  of  the  evidence 
above  provided.  In  the  first  place,  however,  in  order  that  there  may  be  a  better 
understanding  of  the  terms  of  the  problem,  it  will  be  found  expedient  to  review 
briefly  the  characters  of  dentition  known  among  the  more  prominent  types  of 
recent  Chimaeroids,  for  there  is  room  for  the  belief  that  Callorhynchus,  in  spite  of 
its  many  archaic  features,  may  prove  to  have  modified  the  conditions  of  its  dental 
plates,  or  at  least  parts  of  them  (the  '  'tritors ' '),  more  completely  than  some  of  the 
other  forms. 

To  this  end  we  may  compare  the  dental  characters  of  Harriotta  with  those  of 
Rhinochimaera,  as  representing  extreme  types  in  Chimaeroid  dentition.  In  fig.  94  A 
are  shown  in  Harriotta  the  dental  plates  and  the  roof  of  the  mouth;  in  fig.  943  the 
dental  plates,  tongue  region  and  floor  of  the  mouth,  and,  in  figs.  940  and  940, 
corresponding  regions  are  shown  in  Rhinochimaera.  Contrasting  these  forms,  we 
notice  that  in  Harriotta  the  dental  plates  are  studded  with  peg-like  eminences, 
some  of  which,  both  in  the  upper  and  in  the  lower  "jaws,"  form  together  tumid 
tracts  or  ridges.  These  peg-like  eminences,  "tritors,"  are  found  to  pass  deep 
into  the  substance  of  the  dental  plate;  thus,  where  the  plate  is  flattened  and 
more  or  less  transparent,  as  at  the  anterior  margin,  the  peg-like  structures  are 
seen  to  pass  backward,  forming  long  and  narrow  cores.  These  are  evidently  of 
hard,  bony  texture,  for  they  often  stand  out  from  the  plate-like  ridges  when 
the  intervening  basal  portion  of  the  plate  is  worn  away.  We  also  observe  that  the 
adjacent  mucous  membrane  of  the  roof,  sides,  and  floor  of  the  mouth  is  studded 
with  distinct  papillae.  These,  it  will  be  seen,  correspond  to  the  "tritors,"  in 
size,  prominence,  and  closeness  in  arrangement,  and  may,  I  believe,  from  the  evi- 
dence of  similar  structures  in  the  mouth  region  of  various  fishes,  be  looked  upon  as 
homologous  with  tooth-forming  papillae.*  It  will  thus  be  observed,  as  in  figs.  94  A, 
94 B,  that  they  occur  within  the  stomadeal  region;  they  are  absent  in  the  dorsal 
wall  of  the  pharynx;  they  are  present,  however,  on  the  floor  of  the  mouth,  and  are 

*In  a  recently  published  paper  on  the  oral  and  pharyngeal  denticles  of  elasmobranchs  (Proc.  Zool.  Soc.,  1905,  I, 
pp.  41-49),  Imms  gives  reasons  for  homologizing  similar  structures  in  sharks  with  teeth.  He  did  not,  however,  find 
the  papillae  present  in  the  specimen  of  Chimcera  monstrosa  which  he  examined. 


COMPARISON   OF   DENTAL  PLATES. 


121 


continued  along  the  floor  and  sides  of  the  pharynx.  In  Rhinochimaera,  on  the 
other  hand,  the  dental  plates  have  become  thin  and  have  developed  hard  cutting 
edges,  giving  the  mouth  an  almost  beak-like  appearance.  In  the  plates  tritoral 
areas  are  reduced  to  thread-like  elements,  so  delicate  that  they  become  difficult  to 


94* 


Fig.  94. — Dental  plates,  and  roof  and  floor  of  mouth  of :  A,  B,  Harriotta  raleighana.     C,  D,  RhinocHimaera  pacifica. 

distinguish  even  in  the  hard  anterior  pair  of  "vomerine"  plates;  and  in  con- 
nection with  the  obsolescence  of  the  tritoral  areas,  it  is  now  interesting  to  observe  a 
great  reduction  in  the  number  and  size  of  the  papillae  of  the  mouth.  Thus  on  the 
roof  of  the  mouth  there  occur  no  papillae  throughout  the  wide  tract  immediately 
behind  the  palatine  plates. 


122 


CHIMyEROID   FISHES   AND   THEIR   DEVELOPMENT. 


( 


Figs.  95  to    103. — Dental  plates  of  Chimaeroids. 

Fig.  95.  Callorhynchus  "  calloihynctms "  ;   96t  Harriotta  raleighana;  97,  Chimnera  phantasma ;   98,  C.  meditcr- 
r«nea;99.  C.  motubou;    100.  C.  mitsuturii  ;   101.  C.  affinU;   1 02,  C.  colliei ;   1 03,  Rhinochimirra  pacifica. 


COMPARISON   OF  DENTAL   PLATES.  123 

Comparing  now  a  series  of  the  dental  plates  of  Chimaeroids  (figs.  95  to  103), 
we  may  first  place  side  by  side  those  of  Callorhynchus  and  Harriotta  (figs.  95,  96). 
It  then  becomes  clear,  I  think,  that  the  ridges  in  the  dental  plates  of  the  former 
genus  correspond  to  the  clustered  tubercles  in  Harriotta,  a  comparison  which  is 
well  borne  out  by  the  embryological  studies  of  Schauinsland,  for  it  will  be  recalled 
that  the  separate  ridges  of  Callorhynchus  were  shown  to  consist  of  a  mass  of  chalky 
centers  in  which  the  lamellae  of  dentine  were  parallel  to  one  another,  although  their 
substance,  as  was  noted,  remains  uncalcified  (cf.  fig.  105).  A  similar  state  of  affairs, 
it  may  be  remarked,  occurs  in  the  posterior  part  of  the  large  tumid  ridges  in 
Harriotta,  for  these  ridges  and  their  tritors  can  be  readily  sectioned.  On  the  other 
hand,  the  anterior  eminences  of  the  same  tumid  ridges  are  found  to  be  much  harder 
than  the  neighboring  bony  plate,  and  may  with  less  question,  therefore,  be  regarded 
as  representing  true  teeth.  Indeed,  it  is,  after  all,  a  matter  of  minor  importance 
that  these  tritoral  elements  have  never  hardened  in  the  case  of  Callorhynchus;  for 
when  we  consider  the  thickness  and  hardness  of  the  surrounding  bony  plate,  we 
are  led  to  conclude  that  this  may  well  have  usurped  the  function  of  the  separate 
denticles,  and  that  these  therefore  remain  undeveloped.  The  same  rudimentary 
condition  is  probably  true  of  the  minute  tritoral  points  which  one  finds  along  the 
anterior  margin  of  the  vomerine  plates  in  Callorhynchus. 

Continuing  the  comparison,  one  can  with  fair  definiteness  understand  the 
relations  between  the  dental  plates  of  such  forms  as  Harriotta  and  Chimara 
phantasma.  For,  in  the  latter,  the  wide  tritors  at  the  base  of  the  palatine  and 
mandibular  plates  (fig.  97)  are  evidently  homologous  with  the  clustered  tubercles 
in  Harriotta.  In  C.  phantasma,  however,  the  crushing  surfaces  of  the  plate  are 
smoother  and  less  extended.  In  C.  mediterranea  (fig.  98)  the  dental  plates  have 
become  more  oblique  (slanting)  in  their  manner  of  attachment,  the  posterior  flange 
of  the  plates  intruding  deeply  below  the  mucous  fold  in  the  roof  of  the  mouth.  In 
C.  monstrosa  (fig.  99)  the  tritoral  areas  of  the  palatine  plates  are  less  numerous, 
while  in  the  mandibular  plates  they  are  more  abundant,  but  show  less  clearly 
the  peculiar  banded  structure  of  the  foregoing  specimen.  In  C.  mitsiikurii 
(fig.  100)  the  conditions  are  not  widely  different  from  those  in  the  species  from  the 
Mediterranean.  A  peculiar  arching  appears  in  the  palatine  plates,  and  the  ridges 
on  the  posterior  face  of  the  mandibular  plates,  although  smaller,  are  more  con- 
spicuous. In  C.  affinis  (fig.  101)  the  proximal  tritoral  areas  were  not  observed,  and 
altogether  the  grinding  margin  of  the  palatine  and  mandibular  plates  was  narrower. 
In  C.  colliei  (fig.  102),  while  the  tritoral  ridges  on  the  posterior  faces  of  the  pala- 
tine and  mandibular  plates  are  (usually)  conspicuous,  the  grinding  edges  of  these 
plates  are  exceedingly  narrow.  And  in  Rhinochimara  pacifica  (fig.  103),  finally, 
we  attain  a  condition,  as  we  have  already  noted,  in  which  the  tritoral  areas  are 
reduced  to  obsolescence,  the  entire  distal  margin  of  the  plate  functioning  as  a 
cutting  edge. 

From  what  has  already  been  said  regarding  the  dental  plates  in  C.  colliei 
(p.  19),  I  think  we  may  safely  conclude  that  a  wide  range  of  variation  occurs  in  the 
dental  plates  of  Chimaeroids.  Thus  the  tritoral  structures  may  vary  in  number,  size, 


I24 


CHIM^ROID    FISHES   AND   THEIR   DEVELOPMENT. 


and  arrangement;  in  fact,  one  might  even  go  so  far  as  to  maintain  that  from  a  large 
series  of  dental  plates  of  one  species  of  Chimaera  one  might  obtain  variants  which, 
separately  considered,  would  be  placed  with  other  species.  Moreover,  from  the 
function  of  these  crushing  plates,  it  is  not  unnatural  that  marked  differences  should 
appear  in  specimens  of  different  ages  and  from  different  localities  (e.g.,  from  those 
individuals  which  have  lived  upon  different  food  material).  In  short,  we  incline  to 
the  belief  that  changes  in  the  dental  plates  of  Chimaeroids  do  not  predicate  as  wide 
divergences  in  lines  of  descent  as  one  would  naturally  expect.  From  the  standpoint 
of  adaptation,  furthermore,  admitting  the  extreme  value  of  physiological  adaptation 
in  dental  plates  within  the  limits  of  the  present  group,  we  obtain  a  suggestion  why 

phylogenetic  changes 
are  not  recapitulated 
favorably  in  their  devel- 
opment. In  a  form,  for 
example,  like  Callo- 
rhynchus, in  which  the 
basal  (trabecular)  por- 
tion of  the  plates  has 
become  greatly  devel- 
oped in  the  adult,  we 
naturally  expect  that 
there  will  be  less  oppor- 
tunity— shall  we  say 
time  ? — for  the  tritors 
to  recur  in  develop- 
ment in  a  separate  and 
finished  form.  If  they 
do  appear,  they  appear 
regularly  only  in 
form,  soon  to  be  remodeled  or  erased.  Thus  we  find  in 


Fig.  1 04. — Callorhynchus  callorhynchus.  Dental  plates  and  neighboring  mouth  parts  of  late 
embryo  (about  1 10  mm.  long).  After  Schauinsland. 

Fig.  105. — Callorhynchus.  Detail  of  middle  ridge  of  mandibular  dental  plate  of  specimen 
slightly  younger  (about  95  mm.  in  length)  than  the  preceding.  The  dental  ridge  is  seen 
as  a  transparent  object.  After  Schauinsland. 

Fig.  106.  Callorhynchus.  Dental  plates  of  "  larva "  measuring  about  16  cm.  After  spec- 
imen in  museum  of  Columbia  University. 


"family"  or  in  "generic 
Callorhynchus,  according  to  the  figures  of  Schauinsland,  that  these  tritors  do  occur 
in  later  embryonic  stages  (fig.  105),  although  this  author  does  not  refer  distinctly 
to  the  relation  of  dermal  cusps  to  tritors  in  Chimaeroid  plates.  Following  briefly 
the  problem  of  the  dentition  of  Chimseroids,  we  may  again  refer  to  the  presence  of 
numerous  papillae  in  the  mouth  region  of  these  forms.  For,  by  analogies  in  other 
fishes,  these  structures  may  well  represent  rudiments  of  discrete  denticles.  It  is, 
therefore,  of  particular  interest  that  in  the  case  of  Callorhynchus,  where  the  dental 
plates  are  heaviest  and  largest,  we  find  a  corresponding  increase  in  the  size  of  the 
papillae.  For  it  may  be  suggested  that  papillae  which  have  become  calcified  either 
singly  or  in  groups,  have  retained  their  dentitional  (and  ancient)  trend  in  evolution, 
while  those  which  remain  soft  have  survived  because  they  have  undergone  a 
change  of  function.  The  similarity  in  dental  and  non-dental  structures  is  shown 
strikingly  in  the  roof  of  the  mouth  of  Callorhynchus  (fig.  104),  after  Schauinsland. 
That  shown  in  the  roof  of  the  mouth  of  Chimaera  (plate  ix,  fig.  5Oe),  although  not 


DENTAL   PLATES   OF   LARVAL   CHIM^ROIDS. 


125 


as  conspicuous,  is  none  the  less  suggestive  when  we  compare  it  with  the  strictly 
tritoral  conditions  shown  in  Harriotta,  fig.  94  A. 

DENTAL   PLATES   OF   LARVAL   CHIM^ROIDS. 

Furthermore,  if  one  compares  the  dental  plates  in  Chimaeroids  of  different 
stages  of  growth,  one  is  impressed  with  the  evidence  of  larval  adaptations.  The 
plates  of  a  Chimaeroid  recently  hatched  (C.  colliei*)  are  surprisingly  large  in  size, 
but  instead  of  spreading  out  in 
the  form  of  crushing  plates,  they 
protrude  marginally,  forming 
relatively  high  edges  and 
function  evidently  in  cutting. 
Moreover,  the  substance  of  these 
juvenile  plates  is  glassy  (cf. 
Schauinsland,  re  vitrodentine) 
rather  than  horn-like  or  chalky, 
and  their  margins  are  sharp  and 
brittle.  It  is  clear,  therefore, 
that  the  plates  grow  during 
earlier  stages,  notably  at  their 
outer  or  secant  margins,  and  it 
is  a  probable  conclusion  that 
this  condition  of  growth  is  corre- 
lated with  the  special  feeding 
requirements  of  the  young.  In 
later  stages  the  plates  broaden 
and  thicken,  the  secant  edges 
become  less  and  less  conspicu- 
ous, and  gradually  the  tritoral 
areas  appear.  The  latter,  at 


Figs.  107-109. — Harriotta  raleighana.  Dental  plates  (somewhat  diagrammatic) 
of  three  individuals  measuring  respectively  10,  49,  and  64  cm.  At  A  the 
lateral  aspect  of  the  vomerine  and  palatine  plates  is  given. 


least  in  the  species  examined,  are  developed  first  vaguely,  in  extended  tracts  or 
ridges,  and  in  these  there  later  arise  discrete  eminences.  This  is  the  condition 
indicated  above  in  Callorhynchus  (cf.  also  with  fig.  95  the  juvenile  plates  shown  in 
fig.  1 06);  it  is  even  more  marked  in  Chimcera  colliei,  and  it  is  to  be  observed  in 
such  a  form  as  Harriotta.  Of  the  last  form  we  may  introduce  sketches  of  three 
stages  of  the  dental  plates.*  In  the  first  (fig.  107)  the  plates  are  frail,  although 
well  formed,  and  with  secant  prosilient  edges;  they  have  already  ridges  outlined 
and  their  clouded  color  (especially  in  the  palatines)  is  probably  due  to  the  presence 
of  vitrodentine.  In  the  second  stage  (fig.  108)  a  number  of  distinct  tritoral  emi- 
nences appear.  And  in  the  final  stage  (fig.  109),  the  largest  specimen  of  Harriotta 
recorded,  the  tritors  are  well  differentiated. 


*For  the  privilege  of  examining  this  unique  material  the  writer  is  indebted  to  the  United  States  National  Museum. 
He  wishes  especially  to  express  his  thanks  to  its  Assistant  Secretary,  Mr.  Richard  Rathbun,  and  to  its  assistant 
curator  of  Fishes,  Mr.  Barton  A.  Bean. 


126  CHIM^EROID   FISHES   AND   THEIR   DEVELOPMENT. 

From  the  foregoing  characters  in  "larval"  dental  plates,  and  they  are  certainly 
in  the  general  line  of  Carman's  observations,*  we  conclude  that  among  the  many 
specializations  in  the  young  Chimaeroid  may  be  included  a  larval  dentition,  i.  e., 
preceding  the  appearance  of  tritors.  It  may  also  be  remarked  that  the  tritors 
themselves,  when  they  come  to  appear  in  the  different  forms  of  Chimaeroids,  occur 
in  point  of  time  in  interesting  sequence.  In  Callorhynchus  they  appear  in  the 
embryo  (95  mm.),  while  it  is  still  encapsuled,  but  they  fail  to  develop  into  typical 
structures;  in  their  place  there  appear  calcined  ridges  representing  collections  of 
tritors.  In  Harriotta  tritors  become  functional  at  a  period  shortly  after  hatching, 
and  from  this  time  onward  increase  both  in  size  and  number.  In  Chimaera  they 
occur  at  a  later  period,  develop  slowly,  and  even  in  the  adult  are  relatively  few,  and 
the  plates  themselves  early  develop  secant  margins.  In  Rhinochimsera,  finally, 
they  appear  only  in  the  adult,  and  even  then  in  rudimentary  form.  In  the  Chim- 
aeroid series,  there  is  thus,  I  think,  such  evidence  of  progression,  even  in  recent 
forms,  that  we  can  hardly  assume  with  Carman  that  from  a  condition  like  that  in 
Rhinochimsera  arose  the  dental  plates  of  the  other  genera.  On  the  contrary,  in  the 
case  of  Rhinochimaera  we  are  dealing  evidently  with  a  terminal  form,  one  in  which 
the  tritors  fail  to  develop  perfectly  even  in  the  adult,  f 

CONCLUSIONS   CONCERNING   THE   DENTAL   PLATES    OF   RECENT   CHIM^ROIDS. 

A  comparison  of  a  series  of  the  dental  plates  of  recent  Chimseroids,  as  we 
have  seen,  strengthens  the  view  that  these  structures  are  compound,  i.  e. ,  formed  of 
separate  denticle-like  elements,  homologous  with  the  dental  plates  of  certain  sharks, 
e.  £-.,  Cestracjonts.  The  tritors,  according  to  this  view,  represent  dental  eminences, 
simple  or  compound.  But  more  doubtful  is  the  homologue  of  the  dental  plate 
itself.  It  may  represent  either  the  fused  bases  of  teeth  like  the  Cestraciont,  or 
a  structure  entirely  sui  generis,  i.  e.,  fused  by  a  hardening  of  the  connective  tissue 
accumulated  around  the  bases  of  the  true  dental  plates.  According  to  the  observa- 
tions of  Schauinsland  the  embryological  facts  support  more  or  less  distinctly  the 
origin  of  the  tritoral  ridges  from  many  tooth-like  eminences  dentinal  in  structure. 
On  the  other  hand,  the  same  evidence  tends  to  regard  the  substance  of  the  dental 
plate  itself  as  independent  of  the  tritors.  An  examination  of  the  larval  dentition  of 
Chimaeroids  throws,  I  think,  a  side-light  on  the  foregoing  discrepancy,  for  it  is  found 

*Garman,  however,  interprets  these  characters  (Proc.  New  Eng.  Zool.  Club,  1901,  vol.  n,  pp.  75-76)  not  as  larval- 
isms,  but  as  primitive  ;  thus,  according  to  him  "  the  teeth  of  Rhinochimsera  are  of  a  much  less  differentiated  form  than 
those  of  any  other  of  the  recent  genera  of  the  group  ;  that  is,  their  later  stages  are  more  like  the  earlier,  and  presum- 
ably more  like  the  teeth  of  primitive  Chimaeroids  ;  they  approach  those  of  the  extinct  myriacanths  and  the  very  early 
conditions  of  the  teeth  of  other  living  Chimaeroids,  Chimaera,  Callorhynchus,  and  Harriotta.  In  advanced  stages  the 
teeth  of  Harriotta  differ  from  those  of  Rhinochimiera  in  possessing  several  series  of  tritors  which  in  superficial  aspect 
resemble,  in  shapes  and  arrangement,  certain  crowns  of  placodont  teeth.  On  the  teeth  of  Rhinochimaera  there  are  no 
tritors ;  the  teeth  of  the  very  young  of  the  other  living  genera  are  similar ;  this  no  doubt  is  a  mutual  resemblance  to 
those  of  a  common  ancestor,  an  index  to  derivation.  '  To  this  interpretation,  on  the  other  hand,  there  are 

two  somewhat  critical  objections  :  (i)  that  in  Rhinochimaera,  as  this  author  has  later  observed,  there  are  present  tritoral 
points,  small,  it  is  true,  but  tritors  none  the  less ;  and  (2)  that  his  conception  of  the  dental  plates  of  fossil  Chimasroids 
(t.  g.,  Myriacanth)  is  not  valid,  for  whatever  be  the  puzzles  of  the  dental  plates  of  fossil  Chimaeroids  they  have  always 
tritoral  areas. 

fThey  may  be  expected  to  appear  in  a  more  perfect  condition  in  very  old  individuals,  somewhat  as  they  develop  in 
the  late  rather  than  in  the  young  larvae  of  Chimaera. 


SKELETON.  127 

that  the  dental  plates  of  the  adult  are  attained  only  after  a  process  of  metamor- 
phosis, during  which  the  marginally  high,  delicate,  glassy,  and  secant  plates  of  the 
young  are  worn  down  and  give  rise  to  the  adult  dental  plates,  broad  and  thick,  studded 
with  tritors.  Obviously,  therefore,  if  we  accept  the  view  that  a  larval  dentition  is 
present,  it  is  clear  that  the  substance  of  the  dental  plate  can  better  be  regarded 
as  a  "precocious  segregation"  of  the  basal  elements  of  teeth,  i.  e.,  along  the  outer 
marginal  rim  of  the  plates,  than  as  a  new  and  independent  accession  to  the 
materials  of  development.  All  will  admit,  however,  that  the  requisite  proof  of  this 
conclusion  can  be  presented  only  by  paleontology.  On  a  later  page  the  evidence 
in  this  regard  is  summarized. 

SKELETON. 

The  vertebrate  column  of  Chimaeroids  represents,  according  to  Hasse  (1879)  a 
polyspondyly,  which  he  regards  as  typifying  the  ancestral  condition  in  sharks.  The 
column  of  Callorhynchus  was  examined  from  the  standpoint  of  embryology  by 
Schauinsland,  whose  conclusions  I  summarize  as  follows  : 

That  the  early  growth  of  the  chordal  sheath  resembles  that  of  many  sharks, 
inasmuch  as  its  substance  is  invaded  gradually,  and  only  at  few  points,  by  mesen- 
chyme  cells.  That  cartilage  appears  quite  late  in  development.  That  in  each 
segment  (metamere)  appear  both  neural  and  interneural  plates,  as  well  as  corre- 
sponding (i.  e.,  double)  haemal  arches,  especially  throughout  a  greater  portion  of 
the  tail  region.  That  these  cartilaginous  arches  do  not  grow  around  with  their 
bases  the  secondary  chordal  sheath;  this  is  only  overgrown  by  a  stout  sheath  of 
connective  tissue;  the  latter  together  with  the  arches  on  the  one  hand  and  the 
secondary  chordal  sheath  on  the  other  forms  the  secondary  vertebras,  but  the 
secondary  chordal  sheath  is  not  divided  into  separate  (primary)  vertebras — the 
segmentation  of  the  column  being  indicated  only  through  these  parate  arches. 

Schauinsland,  in  brief,  has  been  able  to  find  no  vertebral  centra,  in  the  sense 
in  which  they  occur  in  other  fishes  ;  and  my  own  studies  upon  Chimssra  have  been 
no  more  successful  in  this  important  quest.  No  centra  are  found  in  either  early  or 
late  ' '  larval ' '  stages.  Nor  do  they  occur,  as  I  suspected  they  might,  after  the 
fashion  of  gerontic  structures,  in  very  large  individuals.  At  the  most,  in  the  latter 
case,  there  was  a  fusion  of  neural  and  hsemal  arches  occurring  in  the  region  near 
the  occiput,  but  nothing  which  could  be  interpreted  as  definite  centra.  There  is 
still,  none  the  less,  the  possibility  that  some  form  of  centra  were  represented  in  the 
ancestral  Chimssroid,  and  that  they  were  gradually  lost  in  ontogeny;  indeed,  as  we 
shall  later  note  in  the  Jurassic  Squaloraja  and  Myriacanthus,  centra  appear  to  have 
been  present  in  the  anterior  region  of  the  column  (figs.  138  and  140  c),  where  in  all 
recent  Chimaeroids,  indeed,  the  most  perfect  neural  and  haemal  supports  appear. 

The  development  of  the  skull  has  already  been  illustrated  in  several  stages  of 
Callorhynchus  by  Schauinsland,  and  in  a  single  late  stage  of  Chimaera  by  the 
present  writer.  The  results  of  their  observations  are  briefly  these :  The  chimaeroid 
cranium,  instead  of  developing  as  a  uniform  trough-like  brain-case  (shark),  appears, 
even  in  early  condition,  in  a  wonderfully  complete  form  ;  it  incloses  the  hindbrain, 


128  CHIM/EROID   FISHES   AND   THEIR   DEVELOPMENT. 

the  forebrain,  and  the  nasal  region ;  and  it  early  develops  conspicuous  ridges  which 
evidently  support  and  protect  the  eyes.  And  it  is  the  latter  organs,  it  may  safely 
be  said,  which  have  played  the  most  important  part  in  modifying  the  growth  of  the 
cranium.  For  the  orbital  region  is  of  enormous  size,  occupying  no  less  than  50  per 
cent  of  the  entire  length  of  the  cranium;*  and,  correlated  with  this,  between  and 
above  the  huge  optic  capsules,  the  growth  of  cartilaginous  structures  is  retarded. 
It  follows,  accordingly,  that  while  the  posterior  and  anterior  parts  of  the  chondro- 
cranium  are  well  developed,  its  mid-  or  orbital  region  is  largely  unformed,  and  this 
is,  I  take  it,  the  reason,  the  principal  reason,  that  holocephaly  has  been  developed, 
to  weld  strongly  together  the  anterior  and  posterior  parts  of  the  crani^lm  where  primi- 
tively the  orbital  walls  came  to  be  suppressed  as  the  eyes  increased  in  size.  Certain  it  is 
that  the  wide  palato-quadrate  elements  extend  like  firm  beams  between  the  anterior 
and  posterior  moieties  of  the  skull,  and  afford  at  the  same  time  a  support  for 
the  great  optic  capsules.  And  in  this  result  appears  a  suggestion  why  the  palato- 
quadrates  appear  so  early  and  are  so  large  in  size;  in  fact,  in  no  stage  examined 
has  it  yet  been  found  that  these  palatine  elements  are  altogether  separate  from  the 
cranium.  In  the  earlier  stages  described  (Callorhynchus)  they  are  separate  only  for 
about  half  their  length,  and  from  the  details  of  that  stage  it  is  even  doubtful  whether 
greater  separateness  ever  occurs  in  the  development  of  this  element,  earlier  stages 
showing  probably  a  prochondrial  continuum — very  much  as  one  sees  it  in  the 
prochondrium  of  the  paired  fins  of  sharks.  The  skull  of  the  Chimaeroid,  in  a  word, 
is  specialized  even  in  early  ontogeny ;  witness,  among  other  regards,  the  enormous 
size  of  the  posterior  clinoid  process,  the  huge  fosse  for  the  infundibulum,  the  exag- 
gerated preorbital  processes,  the  median  frontal  crest,  and  the  interorbital  vacuity. 

It  is  true,  on  the  other  hand,  that  certain  skeletal  structures  in  the  chimaeroid 
head  retain  a  primitive  character — possibly  because  they  have  been  spared  func- 
tional changes  by  the  very  fact  that  the  palato-quadrate  element  has  fused  with 
the  cranium.  As  primitive  features  we  may  here  mention:  (i)  The  perfect 
condition  of  the  copulse  of  the  branchial  arches.  (2)  The  presence  of  a  pha- 
ryngeal  element  in  the  hyoid  arch  which  resembles  the  pharyngobranchials  of  the 
hinder  arches.  (3)  The  relatively  large  and  discrete  labial  cartilages,  as  probable 
premandibular  arches,  and  finally  (4)  the  presence  of  a  symphyseal  cartilage  as 
(Schauinsland,  K.  Fiirbringer)  the  probable  serial  homologue  of  a  basihyal.  These 
characters  are  expressed,  slightly  schematized,  in  fig.  in,  and  may  be  compared 
with  the  corresponding  structures  in  sharks  (fig.  110).  In  these  figures  serially 
homologous  parts  are  indicated  by  shaded  or  unshaded  areas. 

It  should  be  mentioned,  in  passing,  that  even  the  branchial  region  of  Chimaeroid, 
in  spite  of  the  foregoing  primitive  characters,  is  not  without  convincing  evidence 
of  precocious  specialization — witness  the  early  appearance  of  the  supporting  extra- 
branchials  of  the  hyoid  arch,  which  are  prophetic  of  the  opercular  flap  of  the  adult. 

The  problem  of  rostral  cartilages  receives  no  evident  solution  in  Chimseroid 
development.  The  anterior  azygous  process  of  selachians,  which  rises  from  the 

*  In  the  skull  of  the  shark  ( e.  g.,  Scyllium )  at  a  corresponding  stage  the  orbit  occupies  about  30  per  cent  of  the 
entire  length  of  the  cranium. 


ROSTRUM,    BRANCHIAL-ARCHES,   FINS. 


129 


nasal  septum  (usually  its  base)  is  probably  represented  in  the  element  which 
Schauinsland  has  figured  as  sp  in  his  plate  xvn,  figs.  1 24,  1 26.  However,  in 
the  Chimaeroid  the  rostral  supports  (rl  and  r2)  later  developed  into  long  and 
separately  jointed  elements.  Quite  doubtful,  on  the  other  hand,  are  the  homo- 
logues  of  the  paired  dorsal  elements  in  the  selachian  rostrum,  those  figured, 
e.  g.,  by  Kitchen  Parker  in  Trans.  Zool.  Soc.,  vol.  x,  plate  xxxvm,  fig.  i,  as  btr; 
they  are  possibly  the  homologues  of  Schauinsland's  elements  ^  in  the  figures  quoted. 
Equally  doubtful  is  the  more  dorsal  azygous  element  (Schauinsland's  rV  v.  the 
present  fig.  in),  which  folds  forward  and  becomes  a  main  support  of  the  produced 
snout  in  Callorhynchus;  it  certainly  finds  no  homologue  in  sharks,  and  in  view  of  the 
history  of  the  frontal  clasping  organ  in  Chimaeroids  (v.  figs.  132-137)  I  am  inclined 
to  interpret  it  as  an  element,  i.  e.,  a  fin  support,  transposed  from  a  hinder  position, * 
a  view  which  is  the  less  difficult  to  accept  when  one  considers  the  metamorphosis 
to  which  the  head  roof  has  been  subjected  by  the  precocious  growth  of  the  eyes. 


M 


Figs.  1 10  and  1 1 1. — Skull  and  branchial  arches  of  Shark  and  Chimaeroid  compared. 

7?1-Z?5,  Branchial  arches;  -B ^f ,  basihyal ;  b tr,  basis  trabecularum  (Kitchen  Parker)  ;  C,  copula;  C/?,  ceratobranchial;  Ell,  Epibranchial; 
H B,  hypobranchial ;  I' ,  "  anteriormost  lip  cartilage  "  (Kitchen  Parker);  Af,  mandible  ;  PR*  pharyngobranchiaL 

The  history  of  the  fins  and  their  supports,  finally,  gives  additional  evidence  as 
to  the  modified  nature  of  later  Chimaeroid  development.  We  may  comment,  for 
example,  upon  the  appearance  of  lobate  dorsal  fins,  the  anterior  with  its  spine,  at 
an  early  period,  and  the  prominence  of  the  paired  fins,  the  pectoral,  for  example, 
having  at  one  time  a  greater  proportional  size  than  in  the  adult.  We  observe  also 
the  precocious  appearance  of  the  mixipterygia  and  the  antero-pelvic  appendages 
(note  especially  plate  ix,  fig.  5of;  also  fig.  90,  and  Schauinsland's  Taf.  xvi,  figs. 
120  and  125),  a  well-marked  character  which  in  such  earl}'  embryos  can  hardly  be 
regarded  as  primitive.  Nor  is  the  plan  of  development  of  the  paired  fins  to  be 
looked  upon  as  yielding  any  evidence  in  favor  of  Gegenbaur's  archipterygium 
theory.  Thus,  the  pectoral,  for  example,  appears  not  as  a  lobate  organ,  contracted, 
shortly  to  bud  out  radial  structures,  but  as  a  lappet  of  a  lateral  fold  which  shows  in 
the  early  stages  distinct  metameral  elements  (cf.  especially  plate  vm,  fig.  49,  and 
Schauinsland's  Taf.  xxiv,  fig.  174).*  The  paired  fins,  in  short,  develop  like  those  of 

*This  translocation  of  anterior  fin-rays  is  by  no  means  uncommon,  associated,  too,  with  change  of  function,  e.  g., 
Lophius,  Autennarius,  etc.     Even  the  sucking  disc  of  Remora  might  here  be  cited. 


130 


CHIMvEROID   FISHES   AND   THEIR   DEVELOPMENT. 


young  sharks,  save  that,  as  in  the  case  of  many  other  chima^roid  structures,  the  rate 
of  growth  is  accelerated;  the  lateral-fold  beginnings  extend  over  fewer  body  segments 
and  are  higher  (proximo-distally),  leading  us  to  conclude  that  in  this  mode  of 
early  fin  growth  the  Chimsroid  exhibits  the  same  relation  to  the  shark  that  the  tel- 
eost  bears  to  the  ganoid.  Especially  convincing  evidence  as  to  the  modified  nature 
of  the  chimsroid  fin  is  produced  by  the  development  of  the  ventral  "claspers";  for 
these,  the  antero-ventral  hooks  and  the  mixipterygia,  are  to  be  regarded  as  highly 
modified  radials.  The  antero-ventral  clasper,  it  is  clear,  has  not  yet  been  evolved 
in  the  sharks,  unless  the  greatly  enlarged  anterior  lappet  of  the  ventral  fin  be 
regarded  as  its  equivalent ;  but  there  is  good  foundation  for  the  belief  that  in 
Chimsroids  between  the  antero-ventral  organ  and  the  compressed  lappet  of  the 


B 


Fig.  1 1 2. — Ventral  fin  and  appendages  in  Chimaera  colliei. 

A,  Fin  of  young  specimen  (31  cm.  in  length)  ;  ventral  aspect  showing  mixipterygia  and  antero- ventral  clasper,  the  latter  still  connected  by  dermal  crease  with  the 
anterior  rim  of  fin ;  C,  mixipterygium  with  lips  unfolded  ;  B,  skeleton  of  foregoing  fin,  showing  the  arrangement  of  the  supports  (radials)  of  the  branches  of 
the  mixipterygium  ;  C,  skeleton  of  fin,  adult :  D,  skeleton  of  ventral  fin  of  Cestracion  (Heterodontus  japomcus),  adult,  for  comparison  with  foregoing. 

pelvic  fin  there  formerly  existed  a  number  of  radialia  ;  witness,  for  example,  the 
rudiments  of  the  segmentation  of  the  basal  plate  from  which  the  antero-ventral 
organ  arises  (fig.  112,  nerve  and  vessel  openings  in  B  and  c),f  or  better  still,  the 
radials  which  persist  in  the  anterior  reach  of  the  fin  of  the  Jurassic  Chima^roid, 
Squaloraja  (fig.  138,  ar).  The  mixipterygium  also  bears  testimony  to  having 
been  closely  connected  with  the  radials  of  the  base  of  the  fin;  thus  in  one  stage  in 
development,  cf.  fig.  1 1 2  B,  the  base  of  the  mixipterygium  bears  rudiments  of 
radialia,  and  the  trifid  tip  is  in  itself  a  relic  of  a  clustering  of  distal  radials.  These 
observations  are  clearly  in  line  with  Jungersen's,  who,  while  admitting  that  the 
"appendix-skeleton  of  the  Holocephales  is  of  less  compound  construction  than  that 
of  Plagiostomes,"  calls  attention  to  the  "wide  separation  of  the  whole  organ  (i.  <?.,) 

*In  the  adult  Chimaeroid  the  basal  articular  element  of  the  pectoral  fin  is  usually  termed  (as  in  Cestracion) 
mesopterygium,  and  it  is  regarded  (Gegenbaur,  1901)  as  including  also  the  propterygium  ;  Schauinsland,  however, 
has  shown  (op.  cit.,  Taf.  xxiv,  fig.  174)  that  the  bibasal  character  of  the  fin  is  due  to  the  obsolescence  of  the 
metapterygium.  The  articular  basal  is,  therefore,  the  propterygium.  With  this  result  the  present  writer  is  in  accord. 

fThis  conclusion  was  originally  suggested  by  Gegenbaur  (1901)  on  the  evidence  of  adult  anatomy. 


VISCERA. 

the  mixipterygium)  from  the  fin  proper ;  the  highly  specialized  form  of  the  primary 
skeletal  parts — against  the  simpler  form  in  the  Plagiostomes  (as  the  simple  rod- 
like  shape  of  the  terminal  joint  *  *  *  ),"  the  presence  of  "particular  copulatory 
organs,"  and  infers  finally  that  "the  Holocephales  by  no  means  occupy  a  primitive 
position  among  the  Selachians."  (Danish  Ingolf  Exped.,  n,  pp.  20-21). 

VISCERA. 

In  the  development  of  its  viscera,  also,  Chimsera  indicates  a  high  degree  of 
specialization.  This,  for  example,  may  be  noted  in  the  following  structures: 

Mesenteries. — No  continuous  mesentery  is  observed  even  in  later  embryonic 
stages  of  development.  Thus,  in  the  embryo  shown  in  plate  vn,  fig.  45,  the 
mesentery  is  clearly  reduced  to  the  string-like  supports  for  vessels  and  ducts  which 
characterize  the  adult.  In  the  same  stage  only  a  rudiment  of  a  ventral  mesentery 
is  present. 

Gut. — In  no  stage  is  the  gut  of  the  same  proportional  length  as  in  the  shark. 
In  the  latter  (Pristiurus)  the  length  of  the  digestive  tract  (measured  from  mouth  to 
anus)  decreases  in  length  between  stages  K  to  o  from  55  per  cent  to  about  50  per 
cent  of  the  total  length  of  the  embryo;  in  Chimaera  in  similar  stages  from  less  than 
30  to  about  15  per  cent.  In  other  words,  the  gut  of  Chimsera  develops  in  a  much 
more  restricted  body  region;  and  from  early  stages  it  appears  as  a  short  tube  of 
wide  caliber.  The  stomach  dilatation,  we  may  thus  conclude,  fails  to  become 
expressed,  and  the  intestinal  valve,  instead  of  undergoing  the  further  spiral  devel- 
opment of  sharks,  makes  but  a  few  turns  (about  four)  and  then  increases  rapidly 
in  the  width  of  the  infolded  band. 

Gills. — The  gills  exhibit  greater  changes  in  their  "metameral"  series  than 
sharks.  Thus  the  hyobranchial  cleft,  even  in  as  early  a  stage  as  K,  is  notably  the 
largest  and  by  stage  o  the  opercular  fold  has  attained  almost  its  adult  proportion. 
On  the  other  hand,  the  fifth  gill-furrow,  although  clearly  indicated,  e.  g.,  stages 
K,  L,  M,  fails  to  become  a  functional  gill-slit.  And  the  spiracle,  even  in  a  favorable 
stage,  is  little  more  than  a  tubular  rudiment;  it  never  develops  respiratory  filaments 
and  is  lost  by  stage  N.  Another  evidence  of  precocious  development  is  shown  in  the 
mode  of  growth  of  the  external  gills.  These  filaments  are  from  the  beginning 
(about  stage  K)  of  large  caliber  (cf.  Schauinsland's  Taf.  xiv,  fig.  no),  i.  e.,  they  at 
once  assume  nearly  their  functional  size.  Accordingly  they  do  not  arise  in  a 
uniformly  developed  vertical  series,  but  on  account  of  their  extraordinary  diameter 
bud  out  one  after  another  as  the  gill-bar  increases  in  size.  Their  later  specialization 
in  developing  blood-producing  dilatations  has  already  been  noted  (pp.  60,  106). 

Kidney. — The  restricted  length  of  the  visceral  cavity  is  accompanied  by  modi- 
fications of  the  excretory  system.  Of  the  pronephros  I  am  unable  at  present  to 
give  a  detailed  account,  and  will  note  only  that  it  is  smaller  and  more  difficult  to 
trace  than  in  the  shark.  The  mesonephric  tubules,  on  the  other  hand,  are  long  and 
coiled  irregularly ;  they  appear  early  and  are  clustered  in  a  deep  stroma  along 
the  dorsal  wall  of  the  body  cavity.  Their  early  condition,  therefore,  does  not, 


132  CHIM^EROID   FISHES   AND   THEIR   DEVELOPMENT. 

embryologically  at  least,  indicate  a  primitive  segmented  condition  (Redecke),  and 
I  am  led  to  suggest  that  the  "segmentation"  of  the  kidney  of  the  adult  arose 
secondarily.  The  absence  of  the  Geschlechtsniere  in  Chimseroids,  moreover,  I  also 
interpret  as  a  secondary  reduction,  an  accompaniment  of  the  enormous  develop- 
ment of  kidney  in  a  short  body  cavity,  a  process  which  caused  an  enlargement  of 
functional  nephric  tubules,  an  obliteration  of  rudimentary  ones,  and  more  direct 
and  special  means  of  carrying  out  gonadial  products.  In  favor  of  the  last  inter- 
pretation are  the  great  size  and  elaborate  regional  differentiation  of  Wolffian  and 
Miillerian  ducts. 

NERVOUS  SYSTEM. 

The  following  features  in  the  development  of  the  system  may  be  mentioned  as 
indicating  that  the  Chimaeroids  have  been  subject  to  wider  changes  than  kindred 
sharks. 

Rcdiiction  of  Cord. — The  cord  in  the  region  of  tail  and  hinder  trunk,  repre- 
senting about  60  per  cent  of  its  entire  length,  is  greatly  modified.  Contrast  in  this 
region  the  diameter  of  the  cord,  its  histological  differentiation,  the  size,  number, 
and  character  of  the  roots  of  the  spinal  nerves.  The  flattening  of  the  cord  in  the 
hinder  trunk  and  tail  region  is,  therefore,  hardly  to  be  compared  to  the  condition 
in  Cyclostomes. 

Flexure  of  Brain. — In  Callorhynchus  (cf.  Schauinsland's  Taf.  xxn)  the  brain 
shows  extraordinary  flexures;  in  the  region  of  the  midbrain  its  axis  changes  direc- 
tion by  almost  180°. 

Size  of  Infundibrihim. — In  early  stages  the  infundibulum  attains  great  size; 
and  concomitantly  the  dorsal  wall  of  the  diencephalon  is  compressed  between  the 
forebrain  and  the  optic  lobes. 

Separation  of  Hemispheres. — In  this  regard  the  early  condition  is  more  marked 
than  in  any  other  fish-like  vertebrate.  Observe  also  the  separation  of  the  entire 
forebrain  from  the  midbrain.  This  in  Chimaera  begins  in  early  stages  and  in  the 
adult  attains  remarkable  proportions. 


III.  FOSSILCHIM/EROIDS: 
THEIR  SIGNIFICANCE  IN  THE  STUDY  OF  RECENT  FORMS. 


The  evidence  of  paleontology  in  the  problem  of  Chimseroid  descent  is  import- 
ant, although  one  must  frankly  admit  that  it  is  still  lacking  in  essential  details,  for 
not  only  are  fossil  Chimaeroids  rare,  but  they  occur  with  but  few  exceptions  in 
fragmentary  form. 

An  outline  of  the  distribution  in  time  of  the  genera  of  Chimaeroids  is  shown 
at  the  bottom  of  page  134.  In  this  has  been  omitted  reference  to  the  supposed 
Silurian  Chimseroid  Dictyorhabdus  prisons  Walcott,  for  reasons  which  are  stated 
below.  Among  the  genera  given,  it  will  be  seen  that  three,  doubtfully  Chimseroid, 
are  Devonian,  representing  together  about  16  species;  one,  probably  a  Chimseroid, 
is  Permian,  and  four  are  exclusively  Jurassic.  From  this  time  onward  the  greatest 
number  of  genera  flourished  in  the  Cretaceous,  representing  at  least  50  species,  and 
one  of  these  genera,  Ischyodus,  extends  from  the  Jurassic  into  the  early  Miocene. 
Another,  a  Cretaceous  genus,  Callorhynchus,  is,  as  we  have  seen,  represented  by 
half  a  dozen  species  at  the  present  time. 

With  this  plan  of  distribution  in  mind,  we  may  summarize  our  knowledge  of 
fossil  Chimaeroids  with  reference  especially  to  their  advancing  characters. 

THE  QUESTION   OF  A  SILURIAN   CHIMSEROID. 

Palaeozoic  Chimseroids  claim  evidently  our  closest  attention,  and  we  should 
consider  first  of  all  the  question  of  the  "fossil  Chimseroids"  described  by  Walcott  in 
1885.  At  Canon  City,  Colorado,  in  the  Ordovician  (Upper  Silurian),  the  United 
States  Geological  Survey  obtained  a  number  of  narrow,  ribbon-shaped  fossils  which 
were  described  by  Walcott  as  Dictyorhabdus  prisons,  and  were  regarded  provision- 
ally, on  account  of  their  general  shape  and  transverse  striation,  as  vertebral 
columns  of  a  chimseroid  fish.*  In  spite  of  the  relative  abundance  of  these  fossils, 
however,  no  Chimaera-like  dental  plates,  spines,  or  kindred  structures  were  found, 
a  condition  the  more  remarkable  since  in  the  matrix  there  occur  innumerable  frag- 
mentary "fish"  remains.  It  is  therefore  doubtful  whether  so  delicate  a  structure  as 
the  vertebral  column  of  a  Chimseroid  would  be  preserved  if  no  traces  were  present 
of  associated  spines,  heavier  cartilages,  and  dental  plates.  The  chimaeroid  nature 
of  the  fossils,  moreover,  becomes  more  doubtful  still  if  they  are  closely  scrutinized. 

*Walcott,  it  should  be  stated,  refers  doubtfully  to  their  chimaeroid  nature.  The  "correlation  is  based  entirely 
upon  the  resemblance  between  the  fossil  form  and  the  calcined  sheath  of  Chimccra  monstrosa.  This  resemblance  is 
too  striking  to  be  passed  over,  although  there  are  certain  differences  that  render  it  of  less  value  in  classification  than 
at  first." 

133 


134 


CHIM^EROID  FISHES  AND  THEIR  DEVELOPMENT. 


In  the  type  specimens  (e.  g.,  one  shown  in  fig.  113)  we  note  that  the  calcified 
"rings,"  which  were  compared  to  the  "centra"  of  Chimaera,  are  not  rings  at  all, 
in  the  sense  that  they  occur  in,  for  example,  Squaloraja,  but  suggest  rather  a  series 
of  more  or  less  irregular  lines  of  growth.  These,  indeed,  are  not  transverse  to  the 
long  axis  of  the  fossil,  but  at  one  side  pass  obliquely  into  root-like  processes,  com- 
pared by  Walcott  to  "lateral  rib-sockets  or  supports,"  structures  which,  it  must  be 
admitted,  are  altogether  unknown  in  chima^roid  anatomy.  The  foregoing  evidence, 
accordingly,  seemed  inadequate  for  associating  this  fossil  with  Holocephali,  and  an 
examination  of  the  types  in  Washington  did  not  yield  me  any  more  convincing 
basis  of  comparison.  Nevertheless  the  very  suspicion  of  a  Silurian  Chimaeroid  was 
of  sufficient  interest  to  warrant  an  attempt  to  secure  more  perfectly  preserved 
material. 

Accordingly,  in  1896,  I  took  the  opportunity  of  visiting  the  type  locality,  and 
may  now  add  the  following  details : 

The  horizon,  the  age  of  which  is  now  generally  admitted  to  be  Ordovician,  was 
readily  located,  and  Dictyorhabdus  was  found  to  be  fairly  abundant.  A  day's 
collecting  trip  made  in  company  with  Mr.  Burbadge  of  Canon  City,  to  whose  kind 
guidance  I  am  greatly  indebted,  resulted  in  obtaining  about  a  dozen  "columns"  in 
lengths  averaging  between  one  and  two  inches,  together  with  numerous  fragments; 

Distribution  of  Chimceroids  in   Time. 


j 

B 
I 

C/3 

"o 

d 

55 

Devonian. 

Carboniferous. 

Permian. 

Triassic. 

1 
Jurassic. 

Cretaceous. 

Eocene. 

Miocene. 

Pliocene. 

(2 

Rhynchodus  

5 

Squaloraja  

Chimaeropsis  

Ischyodus  (  —  Aletodus)  

27 

x 

?x 

Leptomy  lus  

Klasmodectes  

I 

Rhinochimaera  

Chimaera  

8 

DEVONIAN    CHIM^ROIDS. 


135 


and  upon  a  closer  examination  of  these  remains,  I  was  more  than  ever  convinced 
that  they  could  not  be  associated  with  a  Chimaeroid.  In  the  first  place,  in  well- 
preserved  specimens  the  striae  are  sometimes  continued  longitudinally  above  the 
"rib  sockets,"  showing,  in  other  words,  that  they  were  absolutely  unlike  vertebral 
centra.  (Cf.  fig.  114,  /.)  Furthermore,  and  this  is,  I  believe,  most  convincing, 
several  of  the  fossils  showed  a  delicate  flaring  out  at  one  end,  like  the  mouth  of  a 
trumpet,  which  at  once  suggested  the  lip  of  a  molluscan  shell ;  a  character  in  any 
event  distinctly  non-vertebrate,  not  to  say  un-Chimseroid.  I  am  also  permitted  to 
state  that  it  was  the  view  of  Professor  Cope,  to  whom  my  specimens  were  shown, 
that  the  "columns"  could  have  nothing  to  do  with  vertebrates.  It  is  probable,  on 
the  other  hand,  that  they  represent  fragments  of  the  shells  of  mollusks,  possibly 
Cephalopods.* 


Figs.   113  and    114. — "Vertebral  columns"  of  "Silurian  Chimaeroid,"  Dictyorhabdus 

priscus  Walcott.     The  first  figure  after  Walcott. 
t,  oblique  laminar  in  the  structure  of  the  fossil,  suggesting  lines  of  growth. 


Fig.  115.— Dental  plates  of  Men- 
aspis  armata  =  Chalcodus  (permi- 
anus).  Kupferschiefer.  After  spec- 
imen in  Berlin  Museum. 


DEVONIAN  CHIJVL-EROIDS. 

Chimaeroid  remains,  or,  more  accurately,  what  are  generally  accepted  as  such, 
are  widely  distributed  throughout  the  middle  and  especially  the  upper  Devonian 
rocks  of  northern  Europe  and  North  America.  These  are  referred  to  the  family 
Ptyctodontidae,  Unfortunately  for  accurate  diagnosis  the  fossils  are  fragmentary 
and  the  best  results  which  can  be  obtained  from  them  are  briefly  these:  That  in  the 
three  genera — all  at  present  known — Ptyctodus,  Rhynchodus,  and  Palaeomylus, 
dental  plates  were  present  which  resemble  closely  those  of  Chimaeroids.  On  the 
other  hand,  these  plates  were  only  four  in  number  and  their  tritoral  characters  are 
puzzling.  Within  the  substance  of  the  plate  appear  not  a  few  tubercular  tritors, 
but  a  general  series  of  tritoral  points,  sometimes  arranged  in  lamellae,  which  in 
turn  may  form  a  series  of  flat  or  curving  surfaces  tritoral  in  function.  The  tritoral 
points  are  most  conspicuous  in  Ptyctodus  (fig.  116),  where  they  form  lamellae.  In 
Palaeomylus  (fig.  117)  they  spread  out  diffusely,  and  in  Rhynchodus  (fig.  118)  are 
drawn  together  close  to  the  rim  of  the  plates,  forming  thus  an  extended  sectorial 


*The  cephalopod  nature  of  Dictyorhabdus  was  early  commented  upon  by  Hyatt,  a  reference  which  I  had  over- 
looked and  for  which  I  am  recently  indebted  to  my  friend,  Dr.  C.  R.  Eastman. 


136  CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 

margin.  These  conditions  are  shown  in  lateral  (outer)  aspect  in  figures  126-129. 
It  may  be  added  that  there  have  been  found  (Eastman)  a  few  detached  plates 
of  Ptyctodus  (in  the  Hamilton  limestone)  resembling  those  of  Myriacanthus  as 
figured  by  Woodward  (Cat.  Foss.  Fishes,  vol.  2,  pi.  2,  fig.  2,  a).  Also  that  in 
Rhynchodus  the  shape  of  the  meckelian  cartilage  is  known  (fig.  127).  These  char- 
acters, it  will  be  seen,  yield  strong  evidence  in  favor  of  their  chimseroid  nature. 
On  the  other  hand,  we  must  admit  the  possibility  they  may  yet  have  belonged  to 
some  early  specialized  offshoot  of  a  selachian  stem  which  may  not  have  given  rise 
to  true  Chimseroids.  Thus  they  may  have  greater  affinity  with  the  Sandalodonts, 
in  which  very  similar  tritoral  points  occur,  or  to  Deltodonts  or  Cochliodonts,  forms 
which  on  fairly  strong  evidence  are  regarded  as  selachian.  As  to  Ptyctodontids  it 
must  frankly  be  admitted  that  there  is  nothing  accurately  known  as  to  the  form  of 
body,  character  of  fins,  and  the  possession  of  spines.  In  the  latter  regard,  however, 
it  is  fairly  probable,  as  Eastman  and  others  have  shown,  that  the  spine  Phlyctsena- 
canthus  is  to  be  regarded  as  belonging  to  Ptyctodus.  And  it  is  not  impossible 
that  Belemnacanthus  and  Heteracanthus  were  associated  with  members  of  this 
group.  Harpacanthus  and  Cyrtacanthus  may  also  have  belonged  to  a  Chimgeroid. 
But  spines  of  this  character,  we  must  admit,  might  be  associated  almost  equally 
well  with  cestraciont  sharks. 

The  main  virtue  in  the  study  of  Ptyctodontids  is  to  the  writer  this — that  they 
present  some  evidence  (i)  that  Chimaeroids  are  of  Devonian  stock;  (2)  that  at  this 
early  period  their  dental  plates  were  still  but  four  in  number,  representing  the 
dental  structures  of  the  jaw  halves  of  sharks;  and  (3)  that  the  tritors  existed  as 
small  points  forming  together  a  texture  in  the  dental  plates  which  is  well  known 
among  early  sharks.  The  evidence,  in  short,  leads  us  to  conclude  with  fair  proba- 
bility that  the  vomerine  plates  of  Chimseroids  were  a  later  acquisition. 

In  connection  with  these  earliest  "Chimseroids"  there  should  be  mentioned 
the  obscure  group  of  Petalodontids,  which  occur  abundantly  throughout  the  Carbo- 
Permian  and  were  in  some  regards  Chimsera-like,  though  it  is  more  probable  that 
they  represented  forms  of  sharks  which  were  not  closely  related  to  the  ancestral 
Chimseroid,  but  were  rather  examples  of  parallelism.  It  is  none  the  less  noteworthy 
that  in  such  a  form  as  Janassa  the  dental  arrangement,  although  still  retaining 
discrete  elements,  suggests  the  formation  of  tritoral  plates.  Thus,  we  find  that  the 
dental  elements  are  crowded  into  the  axial  line  of  the  mouth  and  are  here  provided 
with  interlocking  ridges,  which  might  well  serve  as  the  point  of  departure  for  the 
evolution  of  tritors.  In  this  event,  the  tritoral  points  would  represent  not  each  one 
an  individual  tooth,  but  only  a  very  small  portion  of  a  tooth.  It  may  further  be 
shown  that  Janassa  was  singularly  chimseroid  in  the  possession  of  a  stout  jaw, 
thick  and  solid  at  the  symphysis,  and  of  remarkably  large  labial  elements.  Finally, 
referring  to  Jaekel's  reconstruction,  it  may  be  pointed  out  that  Janassa  possessed 
a  distinct  antero-ventral  fin  lappet  which  appears  to  the  writer  to  correspond  more 
accurately  to  the  antero-ventral  clasping  organ  of  a  Chimgeroid  than  to  an  enlarged 
fin  ray  of  Raja,  with  which  Jaekel  compares  it.  In  short,  there  is  at  least  the 
suggestion  that  in  such  a  form  as  Janassa  was  represented  a  shark  which  had 


FOSSIL   CHIM^EROIDS. 


137 


Figs.  1 16-120.— Association  of  denial  plates  of  early  Chimaeroids. 

I  16,  Ptyctodus,  restored  dentition,  after  specimens  in  Museum  ol  Comparative  Zoology,  Cambridge,  Mats. 

117,  Paleeomylus,  after  specimens  in  Newberry  collection,  American  Museum  of  Natural  History. 

I  1 8,  Rhynchodus,  after  specimen  in  Newberry  collection,  American  Museum  of  Natural  History. 

I  19,  Myriacanthui,  after  specimens  in  the  British  Museum,  and  in  the  Jermyn  Street  collection  ;  the  tritoral  areas  of  the  two  anterior 

pairs  of  plates  in  the  upper  jaw  are  shown  in  detail  in  fig.  119  A. 
1 20,  Squaloraja,  after  specimens  in  the  British  Museum,  and  in  the  Museum  of  Comparative  Zoology,  Cambridge,  Mass. 


138 


CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 


evolved  a  long  way  in  the  direction  of  the  Chimseroid.  On  the  other  hand,  we 
must  leave  entirely  doubtful  whether  Janassa  was  still  retaining  the  features  of  an 
ancestor  which  gave  rise  to  the  Chimseroid,  or  whether  it  was  a  form  which  was 
becoming  still  more  Chimsera-like  than  its  ancestor — just  as  Lepidosiren  has 
become  more  like  the  amphibian  than  has  the  more  primitive  Ceratodus. 


Figs.  121-125. — Association  of  dental  plates  of  late  mesozoic  Chimeeroids.     Tritors  represented  by  shaded  areas. 

After  specimens  in  British  Museum.     Partly  after  Smith  Woodward. 
121,  Ganodui  ruaulosus ;   122,  Elasmodus  hunteri;   123.  Edaphodon  bucklandi;    124,  Uchyodu:  egertoni ;   125,  Elasmodectcs  willetti. 

The  Permian  fossil  Menaspis  should  also  be  mentioned  in  this  connection. 
Whether,  however,  it  can  be  regarded  as  Chimseroid  has  already  been  considered 
by  the  present  writer  in  a  recent  number  of  the  American  Geologist  (vol.  xxxiv, 
pp.  49-53).  It  was  there  shown  that  the  size  of  the  dental  plates  of  Menaspis 
(fig.  1 1 5)  indicates  that  the  entire  region  of  the  fossil  inclosed  with  spines  is  to  be 


JURASSIC  CHIM^ROIDS. 


139 


regarded  as  belonging  to  the  head.  It  was  noted,  further,  that  the  peculiar  fibro- 
cartilage  spines,  characteristic  of  Menaspis,  may  be  interpreted  as  homologous  with 
the  so-called  lip  cartilages  of  the  later  Squaloraja;  on  the  other  hand,  the  paired 
head  spines  of  Menaspis  correspond  with  those  later  seen  in  Myriacanthus,  although, 
naturally,  they  were  less  highly  specialized.  If,  accordingly,  Menaspis  proves  to 
be  a  Permian  Chimseroid,  it  certainly  simplifies  the  problem  of  Chimaeroid  descent. 
It  indicates  a  shark-like  form  having  four  dental  plates  (fig.  115),  like  Deltodus  or 
Sandalodus,  and  a  dermal  armoring  which  advanced  pari passu  with  the  develop- 
ment of  the  dentition. 


Figs.  1 26- 1 3 I . — Associations  of  dental  plates  in  fossil  Chimaeroids.     Lateral  aspect. 

126,  Ptyctodus;   127,  Rhynchodus  secans  (attached  to  the  mandibular  dental  plate  is  shown  the  outline  of  the  entire  meclcelian  cartilage)  ; 
1 28,  Paleeoraylus    greenei ;   1 29,  Palfcomylus  crassus ;   1 30,  Myriacanthus  paradoxus ;   131,  Uchyodus. 

JURASSIC  CHIM/EROIDS. 

Our  definite  knowledge  of  early  Chimseroids  does  not,  however,  begin  before 
the  Lias  (Lower  Jurassic),  when  remains  of  Squaloraja  and  Myriacanthus  occur, 
notably  in  the  fine-grained  limestones  of  Lyme  Regis.  In  this  favorable  matrix 
Squaloraja  is  so  perfectly  preserved,  even  in  its  cartilaginous  parts,  that  we  are 
enabled  to  reconstruct  its  essential  characters.  As  shown  in  fig.  138,  it  appears 
as  a  somewhat  flattened  form;  its  vertebral  column  is  strengthened  with  fine, 
closely  set,  ring-shaped  thickenings  which  resemble  those  of  a  typical  recent  Chim- 
aeroid ;  the  cranium  is  autostylic  (Traquair)  and  bears  in  the  male  the  frontal 
clasping  organ,  which  here  is  long  and  spine-shaped  (figs.  137,  137  A,  138,  and  detail 
in  fig.  139),  situated  immediately  in  front  of  the  eyes  and  folding  forward.  The 
orbits  are  large,  and  between  them  the  breadth  of  the  cranium  suggests  that  the, 


140  CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 

brain  was  shaped  like  that  of  a  shark.  Of  dental  plates  (fig.  120)  there  are  three 
pairs;  the  meckelian  and  palatines  resemble  one  another  closely,  thus  suggesting 
the  doubtful  Devonian  forms.  In  front  of  the  palatines  now  occur,  for  the  first 
time  among  Chimaeroids,  a  pair  of  "vomerine"  plates,  oblong  and  tumid.  In  these, 
as  in  the  other  dental  plates,  tritors  occur,  in  the  form  of  conspicuous  lamellae.  The 
mouth  was  probably  delicate  and,  judging  from  the  position  of  the  dental  plates, 
it  opened  widely,  far  more  shark-like  than  in  any  recent  Chimaeroid.  At  either 
side  of  the  mouth  region  appear  three  conspicuous  outgrowths,  fibro-cartilaginous  in 
structure,  forming  together  the  marginal  framework  of  this  region  of  the  head.  These 
structures,  although  shown  in  many  specimens,  are  none  the  less  too  imperfectly 
preserved  to  warrant  a  definite  conclusion  as  to  their  relations.  By  some  authors 
they  have  been  regarded  as  spines,  by  others  as  direct  outgrowths  from  the  trabec- 
ular  region  of  the  cranium.  The  anterior  pair  may  represent  the  paired  rostral 
cartilages  of  recent  forms.  The  two  posterior  pairs  are  possibly  labial  cartilages. 
A  conspicuous  rostrum  is  present,  unjointed  at  its  base,  and  defended  on  the  dorsal 
side  by  marginal  rows  of  stout  dermal  denticles  (fig.  1 39).  Adjoining  the  rostrum 
the  snout  was  narrowed,  and  in  this  region  were  apparently  areas  representing 
the  pellucid  spaces  on  either  side  of  the  rostrum  in  recent  Chimseroids  and  in  such 
selachians,  for  example,  as  Rhinobatus  and  many  rays.  In  the  occipital  region  of 
the  cranium  a  large,  median,  elliptical  fosse  was  present,  at  the  base  of  which  there 
were  probably  openings  into  the  otic  region.  Below  this  fosse  one  can  sometimes 
trace  the  anterior  end  of  the  column,  advancing  into  the  floor  of  the  cranium  as  far 
forward  as  between  the  orbits,  and  showing  even  in  this  region  ring-like  peripheral 
thickenings.  It  is  interesting  in  this  connection  to  observe  that  a  well-marked 
occipital  joint  was  present  between  cranium  and  column,  and  that  in  a  single 
specimen  (Harvard  Museum  No.  1147,  Pal.  Coll.,  which  through  the  kindness  of 
Dr.  Eastman  was  generously  loaned  me)  the  anterior  portion  of  the  column  shows 
traces  of  a  coarser  segmentation,  which  indicates,  outwardly  at  least,  cyclospondy- 
lous  vertebrae  (fig.  138  A). 

In  dermal  characters  Squaloraja  was  distinctly  shark-like.  The  entire  body 
was  covered  more  or  less  thickly  with  shagreen,  and  at  certain  points  the  denticles 
attained  considerable  size,  <?.  g. ,  on  the  sides  of  the  rostrum,  near  the  base  of  the 
clasping  spine  (detail  in  fig.  139),  along  the  sides  of  the  tail,  on  the  dorsal  side, 
near  the  base  of  the  paired  fins,  on  the  clasping  organs,  and  almost  as  spines  in  the 
suborbital  region.  Here  they  form  so  firm  a  mass  that  the  ring  below  the  eye  is 
preserved  as  a  conspicuous  character  of  the  fossil. 

Girdles  and  the  cartilaginous  supports  of  the  paired  fins  are  distinctly  Chimae- 
roid, e.  g.,  in  location  and  proportions.  The  stoutly  developed  shoulder-girdle  is 
similar  in  form  to  that  of  a  recent  genus;  it  is  not  known  whether  the  bi-basal 
arrangement  of  the  basalia  occurs  in  the  pectoral  fin,  but  it  is  certain  that  the  radial 
cartilages,  about  30  in  number,  are  arranged  in  a  manner  strikingly  like  those  of 
Chimaera;  their  marginal  extension  was  also  modern  in  plan.  In  the  ventral  fins,  on 
the  other  hand,  more  conservative  conditions  prevail,  for  the  radial  cartilages  were 
probably  1 8  to  20  in  number  (about  one-third  more  numerous  than  in  recent  forms), 


JURASSIC    CHIM^ROIDS. 


141 


and  extended  in 
their  lines  of  attach- 
ment forward  as  far 

as  the  antero-lateral  clasping  organ.* 
This  is  of  particular  interest,  since  it  in- 
dicates, as  we  have  already  noted,  that 
the  antero-lateral  clasping  organ  was 
probably,  as  Gegenbaur,  Carman,  and 
Agassiz  suggested,  a  modified  radial  car- 
tilage (possibly  a  number  of  radial  car- 
tilages), but  up  to  the  present  time 
there  has  been  no  evidence  which  has 
bridged  the  wide  gap  between  the  antero- 
ventral  clasper  and  the  true  radial 
cartilages.  The  condition  of  the  mixip- 
terygium  is  also  significant,  for  it  is  here 
short  and  wide,  its  base  in  one  specimen 
suggesting  clearly  its  origin  in  a  cluster 
of  radial  cartilages.  One  observes,  also, 
that  the  shagreen  which  encases  this 
organ  is  not  limited  to  its  tip,  but  extends 
proximally  almost  to  its  base,  a  condition 
which  has  been  retained  so  completely 
in  no  living  Chimseroid.  It  may  be 
noted,  finally,  that  a  mucous-canal  sys- 
tem is  present  whose  supports  are 
arranged  in  rouleaux  of  minute  rings,  a 
condition  which  exists  in  a  somewhat 
rudimentary  form  in  recent  genera. 

Summarizing,  then,  our  knowledge 
of  Squaloraja,  we  find  that  this  early 
Chimseroid  was  shark-like  in  the  follow- 
ing regards:  (i)  In  dermal  defenses, 
exhibiting  as  it  does  an  investiture  of 
shagreen.  (2)  In  the  width  of  the  mouth, 
which  shows  definitely  that  it  had  not 
yet  attained  the  beak-like  character  of 
the  mouth  of  recent  forms.  (3)  In  the 
undifferentiated  condition  of  the  clasp- 
ing organs.  The  frontal  clasper  is  still  a 


133 


135 


Figs.    132-137. — Evolution  of  frontal  clasping  spine  of  Chim- 
aeroids. 

132,  I'm-spmeof  Myriacanthus.  133,  Frontal  clasping  spine- of  Squalo- 
raja. 134,  Frontal  clasping  spine  of  Myriacanthus.  1 34  A,  Base 
of  clasping  spine  of  Myriacanthus,  ventral  aspect,  to  show  areas  of 
attachment  of  muscles.  135,  Frontal  clasping  spine  of  Ischyodus, 
after  specimen  in  Munich  Museum.  136t  Frontal  clasping  spine 
of  Chimera,  after  section  given  by  O.  M.  Reis.  1 37,  Frontal 
clasping  spine  of  Squaloraja,  dorsal  aspect.  I37A,  Ventral  view 
of  base,  showing  areas  of  attachment  of  muscles. 


*This  wasobserved  by  the  writer  in  a  specimen  (P  2276)  in  the  British  Museum  earlier  described  by  Smith  Wood- 
ward. Dr.  Woodward  did  not,  however,  note  that  these  clasping  organs  were  present,  although  figuring  them  as 
"remarkably  strong  prepubic  processes."  Each  clasper  has  appended  denticles,  of  which  as  many  as  eleven  were  prob- 
ably present.  The  same  specimen  has  preserved  in  outline  visceral  structures,  apparently  testes  and  vasa  deferentia. 


142 


CHIMyEROID   FISHES   AND   THEIR   DEVELOPMENT. 


s 


\ 


spine,  figs.  137  and  137  A,  resem- 
bling closely  the  dorsal  fin-spine  of 
many  sharks  (no  second  dorsal 
spine  or  even  a  dorsal  fin  is  known 
in  Squaloraja,  a  condition  which 
suggests  that  this  form  may  have 
been  bottom-living  and  that  the 
dorsal  fin  may  have  become  shifted 
into  the  region  of  the  tail).  The 
antero-pelvic  claspers  are  shown 
by  the  presence  of  neighboring 
radial  cartilages  to  be  reasonably 
deduced  from  such  elements,  and 
the  short,  wide,  shagreen-coated 
mixipterygia  are 
~"\  also  shark-like  in 

pattern.  Their 
derivation  from 
radial  cartilages 
is  also  indicated. 
^''  On  the  other 

hand,  Squaloraja 
gives   no   positive  ground  for 
the  belief  that  the  fine  rings 
in  its  vertebral  column  are  the 
homologues   of    selachian 
centra.     For   in   this    Liassic 
form    they  are  nearly  as  nu- 
merous as  in  the  living  genera, 
and  the  best  evidence  that  they 
are  derived  from  metameral  centra  is  that 
the  rings  become  slightly  reduced  both  in 
number  and  in  diameter  in  the  region  just 
behind  the  occiput.* 

Fig.  138. — Squaloraja  polyspondyla.  Details  and  partial  restoration. 
After  specimen  P  2276  in  British  Museum,  figured  by  Smith  Wood- 
ward (1886). 

The  narrowing  of  the  snout  is  indicated  in  specimen  No.  1 147  in  Harvard  Museum  and  in  an  undescribed  specimen  in  the  Museum  of  Science  and  Arts,  Edinburgh. 
Fin  outlines  hypothetical.  Details  of  dermal  tubercles  are  shown  in  A  and  ^?.  In  C*the  ventral  occipital  region  is  figured  after  the  above-noted  specimen  of 
Harvard  Museum.  Here  the  condylar  region  is  admirably  preserved  ;  behind  it  centra  appear  at  the  right,  neural  arches  at  the  left.  And  "ring "  vertebrae 
apparently  grade  into  metameral  centra.  «>'»  anterior  radial* ;  tni.r,  mixipterygtum;  '"V,  antero-ventral  clasper ;  oc,  occipital  condyle;  r,  anterior  "ring 
vertebrae"  ;  d,  tract  of  enlarged  dermal  denticles. 


*Since  the  foregoing  was  written  additional  light  has  been  thrown  upon  the  question  of  metameral  segmentation 
in  the  column  of  Squaloraja;  in  the  Harvard  specimen  already  referred  to,  a  coarse  segmentation,  which  suggests 
outwardly  cyclospondylous  vertebrae,  is  well  shown  in  the  postoccipital  region,  fig.  138  c.  It  is  not  certain,  however, 
that  these  coarse  segments  are  serially  homologous  with  the  fine  rings  in  other  parts  of  the  column  :  it  is  possible,  as 
embryology  indicates,  that  they  belong  to  the  outer  chordal  sheath. 


JURASSIC    CHIM^ROIDS. 


The  second  Jurassic  Chimaeroid,  Myriacanthus,  is  known,  unfortunately,  in 
less  detail.  Nothing  has  been  definitely  ascertained  regarding  its  general  shape  or 
the  structures  of  its  trunk.  But  what  is  known  of  its  head  region  shows  that  it 
possessed  extraordinary  features.  The  form  of  the  head  was,  in  general,  like  that 
of  Callorhynchus,  terminating  in  a  long  snout.  This  had  a  somewhat  foliaceous 
tip  (fig.  140),  as  in  the  recent  genus,  but,  on  the  other  hand,  was  broader,  less 
acutely  pointed,  and  studded  dorsally  with  shagreen  denticles  and  dermal  plates. 

The  best  example  of  a  snout  of  Myriacanthus  belongs  probably  to  a  specimen 
in  the  Jermyn  Street  collection,  of  which  a  sketch  is  given  in  figure  141.  The 
figure,  which  shows  the  snout  in  dorsal  aspect,  indicates  also  the  spine-like  nature 
of  the  frontal  clasping  organ.  This  organ  is  shown  again,  in  lateral  view  in  fig.  133. 
There  can  be  little  question  that  in  this  genus  the  shagreen-like  defenses  seen 
in  the  head  of  Squaloraja  are  replaced  by  a  number  of  conspicuous  pairs  of 
dermal  plates,  some  of  which  attain  a  large  size  and  are  furnished  with  spinous 
outgrowths.  Thus,  for  example,  on 
either  side  of  the  jaw  (slightly  schem- 
atized in  fig.  142)  there  is  a  conspic- 
uous "trachyacanthid  "  spine  bearing 
a  large  serrate  row  of  four  or  five 
subspines.  These  elements,  it  may 
be  remarked,  are  well  shown  in  a 
second  specimen  from  Lyme  Regis, 
in  the  Jermyn  Street  collection,  and 
in  Egerton's  type  specimen  of  Prog- 
nathodus  gucntheri  {Myriacanthus  par- 
adoxus),  now  preserved  in  the  British 
Museum,  in  which  one  of  these 
spines  is  shown  in  situ,  attached  to 
the  broad  jaw.  The  arrangement 
of  the  dental  plates  of  Myriacanthus 

•.*       f     •  fc  \ 

With    tair    aCCUraCy    (fig.     1X9). 


IS 


F;g.  l39.-Squalor.ja.    Detail  of  roshal  spine  of  specimen  P  4323 
in  British  Museum. 

The  dermal  denticles  are  grouped  closely  together,  their  bases  flat  and  greatly  enlarged. 
They  occasionally  become  detached.  a,  the  .car,  in  the  .peamen  indicate. 

The  mandibular  plates  show  foldings  on  the  visceral  face  and  in  these  folded  areas 
appears  the  most  conspicuous  aggregation  of  tritoral  points.  A  somewhat  similar 
condition  prevails  in  the  palatines.  In  front  of  the  palatines,  as  in  Squaloraja, 
there  occurs  a  pair  of  "vomerine"  plates.  These,  however,  instead  of  exhibiting 
a  finely  arranged  series  of  tritoral  points,  present  three  rows  of  larger  tritors, 
somewhat  as  indicated  in  the  restoration  (fig.  1  19  A).  Furthermore,  in  front  of  the 
"vomerines"  (and  this  condition  is  unique  among  all  other  Chimseroids,  fossil  or 
recent)  there  is  a  third  and  still  smaller  pair  of  plates,  showing  faintly  a  series  of 
rows  of  tritors.  Another  puzzle  in  the  dentition  of  Myriacanthus  is  seen  in  the 
region  of  the  mandibular  symphysis,  for  here  occurs  an  azygous  chisel-shaped 
tooth  which  is  known  only  in  this  genus  and  in  the  kindred  Chimseropsis  (cf.  also 
p.  145).  The  restoration  in  lateral  view  of  these  dental  plates  is  shown  in  fig.  130. 
On  the  other  hand,  Myriacanthus,  like  recent  Chimseroids,  was  autostylic,  and  it 


144 


CHIM^EROID   FISHES   AND   THEIR   DEVELOPMENT. 


was  provided  with  a  well-marked  dorsal  fin  which  was  supported  anteriorly  by  a 
spine.  This  fin,  it  may  be  remarked,  is  the  earliest  dorsal  known  in  Chimgeroids, 
and  its  structure,  therefore,  deserves  more  than  passing  mention.  Thus,  as  shown 
in  fig.  140,  and  in  the  series  of  figures,  figs.  143  A,  B,  c,  D,  its  position  is  further 
hindward  than  in  recent  forms,  in  this  regard  suggesting  interestingly  the  condition 
of  shark.  It  is  also  noteworthy  that  the  base  of  the  myriacanthid  spine  is  not 
articulated  to  the  fused  mass  of  anterior  epichordalia,  but  is  still  connected  with  a 
hinder  independent  plate,  b,  which,  we  suggest,  becomes  in  recent  Chimaeroids  the 
articular  process  of  the  anterior  cartilaginous  plate.  A  further  correspondence  with 
a  shark-like  condition  is  noticed  in  the  separation  of  the  fin  basis  into  proximal 
("basal")  and  distal  ("radial")  moieties;  in  recent  Chimseroids  these  are  repre- 
sented by  but  a  single  plate,  c. 

It  should  be  finally  observed  that  the  vertebral  column  of  Myriacanthus,  fig. 
143  B,  shows  anteriorly  a  segmentation  which  reasonably  indicates  the  presence 
of  centra. 


Fig.  140. — Head  region  o(  the  Jurassic  Chimaeroid  Myriacanthus.     After  Egerton's  specimen,  in  British  Museum. 
C,  Centra;  5,  Detached   ventro-median  chisel-shaped  "tooth." 

Summarizing  our  knowledge  of  Myriacanthus,  we  note  that  its  dermal  defenses 
are  far  more  highly  specialized  than  in  Squaloraja,  and  that  it  has  evolved  an  addi- 
tional pair  of  tritoral  plates  in  the  upper  jaw,  as  well  as  a  ventro-median  element 
in  the  mandible.  Furthermore,  that  its  frontal  clasping  organ,  although  still  spine- 
shaped,  is  less  like  a  spine  than  in  Squaloraja  (cf,  figs.  131,  132,  and  133).  On  the 
other  hand,  in  its  dorsal  fin  and  in  its  fairly  evident  vertebrae  it  is  more  distinctly 
shark-like  than  any  other  Chimaeroid. 


JURASSIC  CHIM^EROIDS. 

Chimseropsis,  a  third  Jurassic  genus,  is  known  only  from  the  lithographic  stone 
(Kimmeridgian  =  Upper  Jurassic)  of  Bavaria.  It  resembles  Myriacanthus — as  far, 
at  least,  as  one  can  judge  from  fragmentary  remains.  It  certainly  had  similar 
mandibular  plates  and  the  presymphyseal  chisel-shaped  element.  It  was  provided 
with  a  similar  frontal  clasping  spine  and  an  elongated  snout.  It  had  also  a  series 
of  dermal  plates,  as  in  the  former  genus,  and  in  addition  its  trunk  was  studded 
with  small,  conical,  radially-grooved  denticles. 


Fig.  141. — Myriacanthus  granulatus.      Detail  of  snout  region. 

After  specimen  presented  to  Jermyn  Street  Museum  by  Captain  Ibbetson.     As  indicated  in  dorsal  aspect,  the  snout  is  broad  and  thickly 
studded  with  dermal  tubercles.     The  frontal  clasping  spine  appears  somewhat  in  its  relative  position.     The  dental  plates  are  dissociated. 


Fig.  142. — Mandible  of  Myriacanthus,  viewed  from  in  front. 
Restoration  after  one  of  Egerton's  specimens  in  the  British  Museum. 


Brief  mention  need  only  be  made  of  the  Jurassic  genera  Ganodus  (fig.  121) 
and  Brachymylus,  since  these  forms  are  known  only  by  detached  dental  plates.  It 
is  possible,  however,  that  a  more  or  less  complete  skeleton  of  Ganodus*  is  preserved 
in  the  Museum  at  Northampton  (Smith  Woodward,  1892),  and,  in  this  event,  its 
structures  closely  resemble  Ischyodus.  f 


*This  specimen,  a  male,  lacks  the  rostrum,  but  shows  the  frontal  clasping  organ  ;  of  the  latter  the  base  is  expanded 
transversely,  and  shows,  as  in  Myriacanthus  and  Squaloraja  (figs.  I34A  and  137 A),  a  faint  median  crest  on  its  attached 
face;  its  sides  are  laterally  compressed.  The  column  shows  ring  thickenings.  Its  dorsal  spine  is  slender  and  arched 
(=  Lepracanthus). 

fSince  the  foregoing  was  written  I  have  reexamined  the  specimen  of  "  Ganodus  "  avitus  in  the  Munich  Museum, 
and  am  inclined  to  agree  with  its  determination  as  Ischyodus  by  Reiss  and  Smith  Woodward.  It  is  quite  possible, 
however,  that  this  specimen  will  be  shown  to  represent  a  new  genus  as  soon  as  a  more  definite  knowledge  of  Ischyodus 
is  obtained.  Thus  the  present  specimen  has  small  orbits,  small  snout,  and  large  dermal  denticles,  the  latter  scattered 
widely,  especially  conspicuous  in  the  region  just  anterior  to  the  ventral  fin.  There  is  also  ground  for  the  belief  that  a 
pair  of  dermal  plates  were  present  on  or  near  the  posterior  rim  of  the  mandible. 


146 


CHIMyEROID   FISHES   AND   THEIR   DEVELOPMENT. 


Ischyodus,  the  final  Jurassic  Chimseroid,  deserves  more  detailed  examination, 
since  its  skeleton  has  been  obtained  in  a  condition  of  fair  preservation  in  the  Bava- 
rian lithographic  stone.  From  structural  details,  accordingly,  this  genus  is  known 
to  be  widely  separated  from  Myriacanthus  or  Squaloraja;  and  on  the  other  hand  it 
resembled  closely  recent  forms.  It  was  thus  similar  in  the  shape  of  its  head  and 


D 


R 


Fig.  143. — Anterior  dorsal  fin  and  its  supports. 
A,  Shark,  (Squalid);  B,  Myriacanthus;  C,  Callorhynchus  ;  D,  Cliiiiurra. 

trunk;  its  snout  was  fleshy  and  appears  to  have 
terminated  in  a  flap-like  tip.  Its  dental  plates, 
however,  are  stouter  (fig.  124)  than  in  Chimera, 
and  show  fewer  localized  tritoral  areas.  Its  dor- 
sal spine  was  relatively  short  and  robust,  and  the 
frontal  clasping  organ  is  not  unlike  that  of  recent 
Chimseroids,  save  that  (cf.  figs.  135  and  136)  it 
is  more  prominent  and  its  ventral  margin  has  a 
more  extended  series  of  smaller  denticles.  In 
the  details  of  its  skeleton,  it  strikingly  resem- 
bles recent  forms.  One  may  also  recall  that 
an  egg-capsule,  probably  of  this  genus  (of  a 
new  genus,  Aletodus,  according  to  Jaekel),  has 
already  been  referred  to  in  the  present  paper, 
p.  31.  It  resembles  closely  the  capsule  of  the 
recent  Callorhynchus. 
It  is  clear  that  in  Ischyodus  is  represented  the  advancing  line  of  Chimaeroids, 
for  it  extends  from  the  upper  (probably,  indeed,  from  the  lower)  Jurassic  as  far  as 
the  upper  Chalk,  even  possibly  into  the  Miocene  (?  /.  helvetica),  and  is  represented 
during  this  interval  by  many  species  of  many  sizes.  Some  were  probably  as  small 
as  the  recent  Chimczra  colliei,  others  must  have  exceeded  3  meters  in  length. 


CRETACEOUS    CHIMyEROIDS.  147 

CRETACEOUS  CHIM/EROIDS. 

Chimaeroids,  it  may  finally  be  remarked,  were  at  their  maximum  evolutional 
development  during  the  Cretaceous  period;  they  were  then  represented  by  the 
greatest  number  of  genera  and  of  species  (about  50  species),  a  result  which  may 
well  have  proceeded  from  the  acquisition  in  their  line  of  some  new  "expression 
points";  such,  for  example,  may  have  been  the  apposition  of  meckelian  and  chisel- 
shaped  subnasal  "vomerine"  plates,  which  must  have  added  vastly  to  the  effective- 
ness of  this  type  of  dentition;  also  the  greater  development  of  the  clasping  organs; 
also,  perhaps,  deep-water  adaptations  which  enabled  these  forms  to  enter  a  new  and 
rich  field  for  development.  Certain  it  is  that  these  Cretaceous  Chimaeroids  were 
of  a  distinctly  modern  pattern,  and  one  of  them  is  even  assigned  to  the  recent 
genus  Callorhynchus. 

The  details  of  the  evolution  of  recent  genera  from  their  Cretaceous  ancestors 
are  unfortunately  meager.  Dental  plates  and  spines  are  practically  the  only 
evidence  at  hand  for  comparison.  If,  however,  we  limit  our  studies  to  dental 
characters,  we  can  at  least  conclude  that  their  evolution  has  been  in  the  line  of 
producing  tritors  either  in  marginal  or  in  centralized  arrangement.  In  Ischyodus, 
for  example  (fig.  1 24),  it  will  be  seen  that  some  of  the  tritoral  areas  of  the  palatines 
and  meckelian  plates  are  becoming  localized  near  the  median  line.  In  Edaphodon 
(fig.  123)  the  tritoral  areas  of  even  the  vomerines  are  more  nearly  median;  indeed 
the  only  conspicuous  appearance  of  marginal  tritors  occurs  at  the  tip  of  the  meck- 
elian plates.  Elasmodus  (fig.  122)  indicates  an  interesting  combination,  since  it 
has  developed  both  the  marginal  and  the  median  series  of  tritors.  It  has  thus  a 
dentition  of  a  generalized  character,  and  one  is  not  surprised  to  find  that  it  passes 
over  from  the  Cretaceous  into  the  Eocene.  In  fact,  it  differs  little  from  the  denti- 
tion of  the  recent  Harriotta.  On  the  other  hand,  Elasmodectes  (judging  from  its 
meckelian  plates,  which  alone  are  accurately  known)  represents  a  form  which  is 
specializing  in  the  direction  of  marginal  tritors;  they  are  numerous,  continuous  in 
arrangement,  and  minute  in  size,  and  altogether  the  plates  were  probably  beak- 
like  in  function.  This  type  of  dentition  appears  at  first  sight  too  specialized  to 
have  long  survived.  Nevertheless,  granting  a  continued  reduction  of  these  minute 
marginal  tritors,  and  more  flattened  and  beak-like  arrangement  of  the  plates,  a 
descendant  of  Elasmodectes  might  well  be  represented  in  the  recent  Rhinochimaera. 

As  far,  therefore,  as  a  study  of  the  dental  plates  alone  is  concerned,  one  might 
conclude  reasonably  that  the  recent  genera  were  descended  from  Mesozoic  forms 
in  somewhat  the  following  way:  Callorhynchus  from  an  ancestor  closely  related  to 
Edaphodon,  Chimera  from  Ischyodus,  Harriotta  from  Elasmodus,  and  Rhinochi- 
maera  from  Elasmodectes.  Such  genera,  for  example,  as  the  Cretaceous  Lepto- 
mylus  and  the  Miocene  Mylognathus  are  apparently  already  too  specialized  to  have 
represented  the  ancestral  condition  of  the  living  forms.  There  can  be  no  question 
that,  with  the  exception  of  the  three  genera  first  named,  the  Mesozoic,  Tertiary  and 
recent  Chimaeroids  are  a  single  and  homogeneous  stock.  They  have  none  of  the 


148  CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 

bizarre  features  of  Myriacanthus,  Chimaeropsis,  and  Squaloraja;  no  highly  special- 
ized plates  and  spines  in  the  head  region,  no  spine-shaped  frontal  clasping  organ, 
no  presymphyseal  element,  and  no  second  pair  of  "vomerine"  plates.  Among 
recent  forms,  Callorhynchus,  a  Cretaceous  genus,  has  probably  retained  in  most 
regards  the  striking  characters  of  its  Mesozoic  kindred.  And  it  is  not  to  be 
wondered  at,  therefore,  that  its  developmental  features  appear  more  conservative 
than  in  other  genera.  On  one  side  of  this  early  genus  we  may  place  Chimaera, 
which,  as  we  have  seen,  is  in  many  ways  a  highly  modified  form;  and  on  the 
other  side  would  be  arranged  Harriotta  and  Rhinochimaera,  similar  to  one  another 
outwardly,  but  (on  the  evidence  of  dental  characters)  long  separated  from  a  common 
ancestor. 

It  yet  remains  to  consider  the  probable  relationships  of  the  earlier  forms.  It 
is  clear,  first  of  all,  that  in  the  Jurassic  epoch  there  existed  three  distinct  types  of 
Chimaeroids.  One,  as  we  have  noted,  is  that  of  Ischyodus  and  its  allies,  from 
which  unquestionably  all  recent  Chimaeroids  are  descended.  The  second,  Squal- 
oraja, represents  an  aberrant  and  terminal  group;  it  is  to  its  kindred  as  is  Pristi- 
ophorus  to  sharks.  On  the  other  hand,  one  must  admit  that  it  shows  certain 
characters*  which  ally  it  to  the  stock  from  which  Ischyodus-like  forms  must  have 
arisen.  The  third  Jurassic  type,  represented  by  Myriacanthus  and  Chimaeropsis, 
is  the  most  difficult  to  interpret.  From  present  data  it  can  hardly  have  pictured 
the  ancestral  line  of  modern  Chimaeroids,  for  from  what  we  already  know  of  the 
elaborate  dermal  plates  of  the  head  and  its  "trachyacanthid"  spines,  we  infer  that 
it  was  already  too  highly  specialized  to  have  had  the  evolutional  vigor  to  give  rise 
to  forms  in  which  shagreen-like  conditions  again  occur,  for  such  a  series  would 
present  an  analogy  not  as  close,  e.  g. ,  to  the  descending  line  of  the  sturgeons  as 
to  the  line  of  the  Cestracionts,  in  which  the  modern  form  is  related  only  collaterally 
to  the  elaborately  spined  and  heavily  plated  genera  of  the  late  Palaeozoic.  Espe- 
cially puzzling  are  the  dental  characters  of  Myriacanthids;  for  how  are  to  be 
interpreted  the  symphyseal  chisel-shaped  element  and  the  anterior  pair  of  subnasal 
plates?  One  might  readily  suggest  that  the  former  element  was  developed  on  the 
copula  of  the  mandibular  arch — a  suggestion  which  bears  with  it  a  greater  shade  of 
probability  when  we  consider  the  size  and  importance  of  the  mandibular  copula 
as  recently  described  by  both  Schauinsland  and  the  younger  Fiirbringer.  And 
following  a  similar  line  of  speculation  we  might  maintain  that  the  "vomerine" 
plates  were  developed  on  the  pharyngobranchial  element  of  the  jaw  arch,  just  as 
the  palatine  plates  were  developed  on  the  next  lower  (epibranchial)  element.  In 
support  of  this  hypothesis  we  may  note  that,  as  in  Chimaera  a  pharyngobranchial 
element  is  present  in  the  hyoid  arch,  a  similar  serial  element  appears  also  to  have 
been  present  in  the  mandibular  arch  (cf.  figs.  1 10  and  1 1 1).  A  second  hypothesis- 
hypothesis  may  be  a  little  too  dignified  a  term — is  that  the  "vomerine"  and  "pre- 
vomerine"  plates  of  Myriacanthus  represent  the  palatine  plates  of  premandibular 

*E.  ff.,  number  and  disposition  of  dental  plates,  clasping  organs,  integumental  defenses. 


CRETACEOUS   CHIM^ROIDS. 


149 


gill-arches.  This  view,  it  will  be  seen,  finds  some  support  in  the  remarkable  gill- 
arch-like  character  of  the  labial  cartilages,  and  it  becomes  less  fanciful  when  one 
considers  how  frequently  the  labial  cartilages,  especially  in  Chimseroids,  have  been 
homologized  with  premandibular  arches.  As  far  as  Myriacanthus  is  concerned, 
such  interpretations  are  clearly  favored  by  our  knowledge  of  its  evident  speciali- 
zation in  dermal  defenses,  for  in  such  a  light  it  would  be  not  improbable  that  addi- 
tional dermal  elements  would  be  evolved  and  impressed  into  the  service  of  the 
mouth  parts—/,  e.,  plates  which  may  not  have  been  present  in  the  parent  stock 
from  which  descended  Myriacanthus,  Squaloraja,  and  modern  Chimseroids. 

Moreover,  it  is  worthy  of  mention  that  the  forms  which  are  commonly  accepted 
as  the  earliest  Chimseroids,  the  Ptyctodontids,  have  but  two  pairs  of  dental  plates. 
For  it  might  be  plausibly  suggested  that  these  primitive  forms  had  not  reached  the 
stage  in  evolution  when  the  "vomerines"  (i.  e.,  dermal  elements)  appeared  as 
defenses  for  the  anterior  arch. 

In  accordance  with  the  present  considerations  a  scheme  of  the  evolution  of  the 
genera  of  Chimseroids  may  be  arranged  somewhat  as  on  page  150,  fig.  144. 


150 


CHIM^SROID   FISHES   AND   THEIR   DEVELOPMENT. 


RECENT        Rbinochi macro,       ffarriolta,    Ca/lorhyncbus  Chimacra 


JURASSIC 


.Sharks 


TR1ASSIC 


\ 


\\ 
\\ 


PERMIAN 


Menaspis 


CARBONIFEROUS 


\         \ 


N      N 
Rhynchodus  \    N\ 

Palcpomylus^  ^    \       \ 


DEVONIAN 


Ptyctodus 


Fig.  144. — Phylogeny  of  the  Chimseroids.     Arrangement  according  to  palcontological  data. 


IV.     CHIM/EROIDS  IN  THE  PROBLEM  OF  VERTEBRATE  DESCENT. 

On  the  basis  of  the  foregoing  discussion  we  may  finally  consider  the  critical 
question  whether  Chimseroids  are  to  be  regarded  "as  the  most  primitive  verte- 
brates, or  more  precisely  as  the  least  modified  descendants  of  the  ancestral  cranium- 
and  jaw-bearing  vertebrate?"  Are  they,  in  other  words,  to  be  looked  upon  as 
more  primitive  than  sharks  and  as  "representing  a  lower  plane  in  piscine  evolu- 
tion' '  ?  These  questions  have  been  touched  upon,  more  or  less  distinctly,  throughout 
the  present  paper  and  the  conclusion  has  been  already  indicated.  And  I  think  we 
may  now  state  confidently  that,  from  the  evidence  of  embryology  and  paleontology, 
Chimseroids  represent  not  the  ancestral  vertebrate,  but  rather  a  highly  modified 
group  descended  from  selachian  ancestors.  At  the  present  time  the  evidence  may 
be  summarized  upon  which  this  induction  is  based. 

PALEONTOLOGICAL  EVIDENCE  THAT  CHIM/ERO1DS  ARE  DERIVED  FROM  SELACHIAN 

ANCESTORS. 

(a)    Their  later  origin: 

The  earliest  genera  of  whose  Chimseroid  nature  there  can  be  no  doubt  do  not 
appear  before  the  lower  Jurassic,  and  from  this  horizon  have  been  described  but 
two  genera.  Sharks,  on  the  other  hand,  appear  in  ages  remotely  earlier,  and  they 
are  then  represented  by  several  orders,  many  genera,  and  very  many  species. 
Thus,  in  the  Palaeozoic  alone,  we  may  enumerate  at  least  fifteen  genera  and  forty 
species  whose  shark-like  anatomical  features  are  definitely  known,  and  we  may 
reject  altogether  the  testimony  of  the  numberless  selachian  "species"  of  spines  and 
teeth.  Into  this  limbo  of  indeterminata  may  provisionally  be  cast  Ptyctodonts, 
together  with  Cochliodonts,  Deltodonts,  and  similar  forms.  And  we  may  in  like 
manner  regard  the  Permian  Menaspis  as  doubtful.  But  even  if  we  grant  that  all 
Ptyctodonts  are  Chimaeroid,  we  have  still  the  testimony  that  the  sharks  were 
in  earlier  periods  overwhelmingly  more  numerous  and  more  diversified.  And  we 
have  equally  to  admit  that,  even  at  that  early  period,  many  sharks,  from  horizon 
to  horizon,  modify  the  character  of  their  cuspid  teeth  in  the  direction  of  tritoral 
plates.  In  short,  admitting  the  evidence  of  dentition,  one  may  state  conservatively, 
that  even  in  their  epoch  Ptyctodontids  stood  to  the  sharks,  both  in  number  and 
in  variety,  only  as  one  to  one  hundred.  And  from  this  testimony  alone  we  can 
almost  reject  the  thesis  that  Chimseroids  were  ancestral  sharks.  Unfavorable  to 
the  latter  view,  moreover,  is  the  fact  that  the  culmination  of  the  Chimaeroid  line, 
i.  e.,  in  genera  and  species,  did  not  occur  before  the  Cretaceous,  while  that  of 
sharks  antedated  the  Permian. 


152  CHIMyEROID   FISHES    AND   THEIR   DEVELOPMENT. 

(<$)  Shark-like  morphological  characters  of  early  Chimceroids: 

The  earliest  definitely  known  Chimseroids  were  clearly  shark-like.  In  this 
regard  attention  need  only  be  called  to  the  facts:  (i)  That  they  had  shark-like 
dermal  denticles  scattered  over  the  body;  (2)  a  male  clasping  organ  in  the  form 
of  a  selachian  fin-spine;  (3)  rudiments  of  vertebral  centra  in  the  postoccipital 
region;  and  (4),  in  one  form  at  least,  tritors  in  the  anterior  dental  plates  which 
in  arrangement  resemble  strikingly  the  teeth  of  a  Cestraciont  shark. 

Furthermore,  the  earliest  Chimseroids  present  no  characters  which  can  be 
fairly  interpreted  as  more  primitive  than  those  of  sharks.  They  were,  on  the  con- 
trary, more  modified.  Thus  in  their  males  they  had  already  evolved  the  three  sets 
of  clasping  organs. 

EMBRYOLOGICAL  EVIDENCE  IN  FAVOR  OF  THE  VIEW  THAT  CHIM/ERO1DS  ARE  DERIVED 

FROM  SELACHIAN  ANCESTORS. 

The  riddle  of  Chimseroid  development  can,  I  am  convinced,  be  read  in  only 
one  way;  for  the  evidence  yielded  by  the  various  phases  of  embryology  points  to 
the  modified  nature  of  Chimseroid  descent:  That  is,  if  we  grant  the  value  of  tran- 
sitional stages  in  demonstrating  the  descent  of  the  more  complicated  from  the  less 
complicated  type,  we  may  in  the  present  case  obtain  a  mass  of  evidence  which 
must,  it  seems  to  me,  be  regarded  as  conclusive.  The  scope  of  this  evidence  is 
seen  in  the  following  summary: 

I.  Chimseroids    are    more    complicated    than    sharks    in    sexual    characters. 
Males  differ  from  females  to  a  greater  degree  in  point  of  size  and  proportions,  and 
in  the  development  of  clasping  organs.     Of  the  latter,  sharks  have  only  mixip- 
terygia,   while  Chimaeroids  add   to  these  the  antero-ventral   claspers  (which    are 
modified  anterior  radials  of  the  ventral  fin)  and  the  frontal  organ  (which  is  inter- 
preted as  a  transposed  fin-spine). 

II.  The  egg-capsule  of  the  Chimseroid  is  the  more  complicated.     It  is  larger 
in  proportion  to  the  size  of  the  fish,  and  is  adapted  more  especially  to  the  needs  of 
the  young  fish.      In  this  regard  we  recall  its  remarkable  regional  differentiation 
(i.  e.t  for  head,  trunk,  and  tail  of  the  young  fish),  breathing  pores,  opercular  valve, 
and  organ  of  attachment — characters  more  complicated  than  in  the  egg-capsules  of 
sharks. 

III.  The  early  egg  membranes  are  more  complex  than  in  sharks.      Here  we 
refer  to  the  changes  in  the  tunic  and  the  behavior  of  its  nuclei. 

IV.  The    phenomena    of   fertilization.      As    one    instance  of   complexity    in 
Chimsera  we  recall  that  following  polyspermy,  the  sperm  merocytes  divide  at  once 
amitotically;  while  in  shark  amitosis  is  attained   only  after  a  decadent  series  of 
mitotic  divisions.     Witness  also,  in  the  Chimseroid,  the  peculiar  features  of  the  sperm 
track  and  the  character  of  the  asters. 

V.  Early  cleavage  lines,   as  in  the  case  of   the  (highly  modified)  rays,    are 
suppressed,  and  the  synchrony  of  segmentation  is  soon  lost.     Further  complication 
in  Chimsera  appears  in  the  germinal  wall — in   which  are  confused  yolk-masses, 


SPECIALIZED   CHARACTERS.  153 

small  blastomeres,   merocytes  and  undivided  yolk — and  in  the  periphery  of  the 
blastoderm.    We  find  further  that  amitosis  occurs  plentifully  within  the  blastoderm. 

VI.  The  fragmentation  of  the  egg,   which  begins  at  gastrulation,   doubtless 
arose  as  a    primitive  character,  i.  e.,  holoblastism.     Its  function,  however,  in  the 
modern  Chimseroid  has  become  a  distinctly  complicated  one.      By  this  process  a 
large  part  of  the  yolk  is  diverted  from  its  primitive  use  and  is  appropriated  by  the 
embryo  secondarily,  via  gills  and  gut.      The  yolk-sac,  accordingly,  is  reduced  to 
miniature  size. ' 

VII.  The    embryo  develops    precociously.      While  still  minute  in  size,  i.  e., 
in  terms  of  the  blastoderm,  it  presents  complicated  structures;  when  2.5  mm.  in 
length  it  has  already  25  somites,  and  suggests  the  adult.      Compared  to  the  young 
shark  it  is  also  more  specialized  in  its  relation  to  the  germinal  yolk  and  in  the 
development  of  the  vascular  system.      In  this  connection  note  also  the  differen- 
tiation of  many  types  of  merocytes,  and  the  evidence  that  megaspheres  are  not 
primitive  ova. 

VIII.  The    head  region  of    the  embryo  indicates    precocious    specialization. 
We  thus  note  the  early  appearance  and  great  size  of  the  eyes,  the  appearance  of 
the   cephalic    "hood,"   the  greatly  shifted  position   and  the  reduced  size  of  the 
spiracle,  the  condition  of  the  head  mesoblast,  the  fewer  and  larger  gill  lamellae,  the 
moniliform  character  of  the  external  gills,  due  to  the  presence  of  special  blood- 
producing  organs,  the  reduction  of  the  fifth  gill,  and  the  early  differentiation  of  the 
branchiostegal  flap. 

IX.  The  trunk   region  bears  similar  testimony  in  the  matter  of  precocious 
specialization.     We  thus  observe  the  early  period  at  which  the  greatly  elongated 
tail  is  produced,  the  anterior  position  of  the  anal  region  even  in  early  embryos,  the 
speedy  obliteration  of  the  lumen  communicating  between  myo-  and  splanchnoccele, 
the  early  appearance  of  the  dorsal  fin-spine  and  of  mixipterygia,  the  last  a  feature 
worthy  of  especial  comment,  since  it  indicates  the  appearance  of  secondary  sexual 
characters  in  even  small  embryos.     Also  to  be  noted  is  the  great  size  early  assumed 
by  the  paired  fins. 

X.  Larval  characters  are  also  developed  prominently.     To  be  mentioned  in 
this  regard  are:    Larval  coloration;  larval  proportions  of  head,  trunk,   and  fins; 
appearance  of  greatly  enlarged  dorsal  scales;  larval  dentition,  in  which  the  outer 
rims  of  the  dental  plates  become  specially  developed. 

The  foregoing  are  but  the  most  conspicuous  characters  to  be  selected  from  the 
present  embryological  materials.  Nevertheless  there  can  be,  I  believe,  no  valid 
question  as  to  their  significance;  for  in  no  essential  regard  can  they  be  interpreted 
as  representing  conditions  so  unmodified  as  to  have  given  rise  to  the  present  condi- 
tions in  the  development  of  sharks.  * 


*One  might,  it  is  true,  regard  the  modern  sharks  as  arrested  "  larvae"  of  Chimasroids,  and  thus  maintain  that  shark 
embryos  exhibit  less  complicated  conditions  than  their  ancestral  forms.  But  if  the  diversity  of  specialized  characters, 
as  shown  in  the  foregoing  summary,  is  duly  considered,  this  extreme  view,  it  seems  to  me,  can  only  fall  of  its  own 
weight.  For  in  view  of  the  many  lines  of  specialization  of  Chimaeroids,  it  seems  about  as  improbable  that  these 
forms  could  have  represented  the  ancestral  sharks  as  that  a  bird  could  have  represented  the  ancestral  reptile,  or  that  a 
recent  horse  could  have  been  the  progenitor  of  Protohippus. 


154  CHIM^EROID   FISHES   AND   THEIR   DEVELOPMENT. 

If  this  general  position  be  granted,  we  have  still  to  consider  the  question 
whether  Chimaeroids  actually  possess  any  primitive  characters.  Reviewing  the 
materials  at  hand  I  think  we  may  here  refer  to  the  following: 

I.  Holoblastism. — The  egg  cleaves  totally.     Of  this  there  can  be  no  doubt, 
although,  as  we  have  seen,  this  condition  is  complicated  in  many  ways  (pp.  58-63), 
and  its  retention  is  with  strong  probability  due  to  the  highly  modified  physiological 
needs  which  it  now  subserves.     In  other  words,  the  holoblastism  of  Chimaera  is 
less  primitive  than  adaptive,  and  thus  may  not  represent  the  ancestral  condition  in 
cleavage  of  such  a  form  as  the  shark  Cestracion  (Heterodontus). 

II.  Gastrulation. — The  appearance  of  the  blastopore  in  front  of  rather  than 
at  the  rim  of  the  blastoderm  is,  I  take  it,  of  no  little  significance  as  a  primitive 
character.      Its  retention  is  probably  correlated  with  the  survival  of  a  holoblastic 
type  of  cleavage. 

III.  Primitive  conditions  in  the  mouth  region. — No  one,  I  assume,  will  deny 
that  a  pharyngobranchial  element  in  the  hyoid  arch  is  a  primitive  feature.     And  of 
kindred  significance  are:    The  presence  (i)  of  copular  segments  in  the  branchial 
arches,  (2)  of  a  mandibular  copula,  (3)  of  a  pharyngobranchial  process  in  the  mouth 
arch,   and  (4)  of  more  distinct  "preoral  arches"  than  in  sharks.     On  the  basis  of 
these  characters,  then — and  they  are  clearly  of  no  little  weight — may  we  conclude 
that  Chimaera  pictures  more  accurately  than  shark  the  ancestral  gnathostome?    To 
this  conclusion  there  are  clearly  two  lines  of  objections.     First,  that  in  many  other 
features  Chimaera  is  singularly  modified,  and,   second,  that  the  mouth  region  of 
Chimaeroids  is  the  less  easily  compared  with  that  of  recent  sharks  on  account  of  the 
autostylism  which  has  prevailed  in  the  former  groups  since  (at  least)  Jurassic  times. 
In  other  words,  in  view  of  the  first  objection,  it  would  be  judicious,  I  conclude,  to 
interpret  the  foregoing  remarkable  characters  in  the  mouth  parts  of  recent  Chim- 
aeroids  in  the  following  way  :     That  autostylism,  although  in  itself  a   modified 
condition,  tended  less  to  alter  the  neighboring  branchial  structures  than  did  the 
adaptation  of  a  more  flexible  support  for  the  jaw-hinge  (c.  g.,  as  in  the  modern 
sharks).      And  that  thus,  under  the  partially  conservative  influence  of  autostylism, 
Chimaeroids,  in  spite  of  other  structural  modifications,  have  nevertheless  retained  a 
few  of  the  characters  of  primitive  sharks. 

The  foregoing  conditions  (I,  II,  and  III)  are,  as  far  as  I  am  aware,  the  most 
important  findings  of  embryology  as  to  the  primitive  position  of  Chimaeroids.  Less 
important  in  this  question  are  the  earlier  data  of  morphology  (v.  pp.  4-5).  Thus: 

IV.  Absence  of  ribs. — This  character  becomes  of  minor  importance,    in  the 
light  of  developmental  documents.     The  early  shortening  of  the  visceral  cavity 
would  obviously  be  unfavorable  to  the  development  of  ribs,  even  if  these  elements 
had  been  present  in  the  ancestral  form.     As  to  the  latter  condition,  it  may  be 
mentioned  that  at  the  present  time  there  is  good  reason  for  the  belief  that  in  the 
earliest  sharks  (Acanthodians  and  Cladoselachids)  ribs  were  not  present. 

V.  Stomach,  Kidney,  Mazza' s  Glands. — In  these  structures  also  the  question 
of  primitive  conditions  is  by  no  means  clear.      For  the  early  shortening  of  the 
visceral  cavity  may  readily  have  been  accompanied  by  secondary  modifications  in 
the  viscera. 


CHIM^ROIDS   IN   VERTEBRATE   DESCENT.  155 

VI.  Musculatiire. — The    muscles   of    the   branchial   arches,    like  the    arches 
themselves,  retain  primitive  features;  thus  the  adductor  of  the  jaw  retains  its  inter- 
branchial  character.     On  the  other  hand,  there  is  no  ground  for  the  belief  that  the 
muscles  of  the  shoulder  girdle  are  unaltered;   Gegenbaur  (1901),   for  example, 
frankly  admits  that  they  are  more  modified  than  those  of  sharks,  and  he  calls 
attention  to  the  general  blending  of  the  segmental  muscles  of  the  trunk.     There 
appear  also  in  Chimera  special  muscles  developed  in  connection  with  the  erectile 
spine  and  clasping  organs  which  can  best  be  interpreted  as  derived  from  the  simpler 
elements  in  sharks. 

VII.  Nervous  System. — In  this  connection  it  may  be  remarked  that  some  of 
the    primitive    characters    of    Chimaera — open    lateral    line,    separate  nerve  roots, 
simple  auditory  organ — are  clearly  paralleled  in  sharks,  e.g.,  Notidanids. 

SUMMARY. 

Chimaeroids,  accordingly,  are  widely  modified  rather  than  primitive  forms. 
The  evidence  contributed  by  anatomy,  embryology,  and  paleontology  is  unmistak- 
ably in  favor  of  this  interpretation.  And  there  can  be  no  doubt  that  the  recent 
forms  retain  less  perfectly  the  general  characters  of  the  ancestral  gnathostome  than 
do  living  sharks.  On  the  other  hand,  it  must  be  admitted  that  Chimaeroids  have 
retained  several  characters  of  their  Palaeozoic  selachian  ancestors  which  modern 
sharks  have  lost.  According  to  many  converging  lines  of  evidence  we  may  indeed 
go  so  far  as  to  conclude  that  the  ancestral  Holocephali  diverged  from  the  selachian 
stem  near  or  even  within  the  group  of  the  Palaeozoic  Cestracionts.  *  Indeed,  the 
recent  Chimaeroids  and  Cestracionts  retain  many  features  of  kinship.  Among 
these  need  only  be  mentioned  at  the  present  time  approximations  in  dentition, 
labial  cartilages,  articulation  of  mandibles,  structures  of  fins,  and  urogenital  system. 
Even  the  complicated  egg-capsule  of  Chimaeroids  finds  its  nearest  parallel  in 
the  recent  Cestraciont,  a  comparison  often  lost  sight  of  on  account  of  the  spiral 
arrangement  of  the  lateral  webs  in  the  capsule  of  the  latter  form. 

From  the  standpoint  of  taxonomy,  on  the  other  hand,  it  must  be  clearly  recog- 
nized that  the  Chimaeroids  have  been  separate  from  the  early  sharks  for  so  long  a 
time  and  have  acquired  such  different  characters  that  they  are  to  be  given  a  high 
rank  among  the  divisions  of  the  subclass  Elasmobranchii,  the  equivalent,  let  us 
say,  of  such  groups  as  pleuracanths  or  pleuropterygians.f 

*This  conclusion  recalls  the  remarks  of  W.  K.  Parker,  in  his  paper  on  the  skull  of  cyclostomes  (Phil.  Trans.  1883, 
p.  451)  :  "Even  the  Chimaeroids  come  so  near  the  ordinary  Elasmobranchs  as  to  suggest  that  their  embryology  would 
not  be  so  helpful  (in  the  matter  of  the  descent  of  the  Cyclostomes)  as  one  might  imagine,  especially  if  their  solid  upper 
face  has  been  acquired  as  a  secondary  modification  and  not  a  -primary  condition,  such  as  we  see  in  the  Tadpole,  which 
is  especially  solid  and  largely  continuous  with  the  basis  cranii,  in  the  larval  Aglossal  types,  Dactylethra  and  Pipa. 
(The  interposition  of  those  remarkable  sharks,  Cestracion  and  Notidanus,  between  the  ordinary  kinds  and  the  Chimae- 
roids, makes  the  likelihood  of  the  solidity  of  the  upper  jaw  being  primary  a  very  doubtful  thing  ;  I  once  thought 
otherwise,  but  found  Mr.  Balfour  strongly  set  against  me  in  this  suggestion,. ) " 

t  One  recalls  at  this  point  an  early  remark  of  Huxley :  "For,  considering,  in  addition  to  the  cranial  characters, 
the  structure  of  the  vertebral  column,  and  of  the  branchiae,  the  presence  of  an  opercular  covering  to  the  gills,  the 
peculiar  dentition,  the  almost  undeveloped  gastric  division  of  the  alimentary  canal,  the  opening  of  the  rectum  quite 
separately  from  and  in  front  of  the  urogenital  apertures,  the  relatively  small  and  simple  heart,  the  Chimaeroids  are 
far  more  definitely  marked  off  from  the  Plagiostomes  than  the  Teleostei  are  from  the  Ganoids." 


156  CHIM^ROID   FISHES   AND   THEIR   DEVELOPMENT. 

Of  the  interrelationships  of  the  various  modern  Chimaeroids  enough  has  been 
said  in  the  foregoing  pages;  on  many  grounds  it  is  evident  that  Callorhynchids 
have  retained  more  nearly  the  characters  of  the  ancestral  Holocephali  than  have 
Chimserids. 

If,  finally,  the  data  of  Chimseroid  development  be  carefully  scrutinized, 
there  will,  I  am  sure,  be  found  material  for  interesting  reflection.  For  such  a 
study  brings  with  it  considerations  of  greater  significance  than  the  pedigree  of  a 
group  of  little-studied  vertebrates.  It  touches,  first  of  all,  the  larger  problem  as  to 
the  degree  to  which  embryology  may  be  used  in  determining  the  kinship  of  animals. 
Moreover  it  furnishes  somewhat  definite  illustrations  of  the  processes — usually  so 
obscure — of  "shortening  up"  or  "concentrating"  developmental  stages,  and  of 
embryonic  "specializations."  It  also  contributes,  but  in  a  minor  degree,  to  the 
problem  of  germinal  layers  and,  in  even  a  more  difficult  field,  to  the  interpretation 
of  amitotic  cell-division. 


LITERATURE  LIST. 


LITERATURE  LIST. 


(Omitting  references  to  a  number  of  text-books  and  early  zuorks.) 


CHIM^ROIDS. 
General  and  Systematic. 

1833-44.  AGASSIZ,  L.     Poissons  fossiles.    Texte  III,  pp. 

3-4,  Tab.  C.     (C.  monstrosa.) 
1871.  Reference   to    separation    of    Chimaeroids 

from  sharks,    v.  Wilder,  Proc.  Bost.  Soc.  Nat. 

Hist,  Vol.  XIV,  p.  214. 
1892.  ALCOCK,  A.    Reference  to  "C.  monstrosa,  Linn.?" 

occurring  off  Coromandel  coast.    Indian  Marine 

Survey. 
1613.  ALDROVANDUS.     De  Piscibus.     Liber  IV,  pp.  402, 

403. 

1772.  ASCANIUS,  T.    Icones  rerum  nat.    PL  xv. 
1886.  BEDDARD,  F.  E.     Reference  to  Howe's  view  as  to 

descent   of   elasmobranchs   and   dipnoans    from 

Chimaeroids.     Proc.  Zool.  Soc.  Lond.,  p.  524. 
1870.  BENEDEN,  P.  J.  VAN.     Reference  to  food  of  Chi- 

rmera.    Mem.  Acad.  Roy.  Belg.,  Vol.  XXXVIII, 

in  Les  Poissons  des  Cotes  de  Belgique. 
1839.  BENNETT,  J.    Zoology  of  Capt.  Beechey's  Voyage, 

p.  71,  PL  xxiii.     (C.  colliei.) 
1862-78.  BLEEKER,    P.     Ichthyol.,   IV   part,   p.   69,    PL 

cxxiv.      (C.   monstrosa.) 
1852.  Ichth.,   Fauna  van   Amboyna   en   Ceram, 


1859. 


p.  81. 


Elfde    Bijdrage   Vischfauna    Amboyna. 


1832-42    and    1846.    BONAPARTE,    C.    L.    Iconographia 

Fauna  Ital.   and   Catal.   Pesci  Europei,   No.  82, 

p.  20. 
1823.  BORY  DE  SAINT-VINCENT.     Diet.  Class.  Hist.  Nat., 

Vol.  Ill,  p.  62,  PL  v.     (Cal.  milii.) 
1891.  BRUHL,  C.  B.    Dipnoi-  u.  Holocephalikopf.    4to. 

Pis.  vii.    Wien. 

1898.  BYRNE,  L.  W.     On  the  general  anatomy  of  Chi- 
maera.    Preliminary   notice.      Proc.    Zool.    Soc. 

Lond.,  Jan.  18. 
1898.  Chimaera    monstrosa    in    the    North    Sea. 

Naturalist,  p.  206. 
1872.  CANESTRINI,    G.     Reference    in    Fauna    Italiana. 

Parte  3A,  pp.  61  et  seq. 

1868.  CAPEIXO,  F.  DE  BRITO.     Jour.  Sc.   Math.,  Phys.  e 

Nat.  Lisboa,  Vol.  LV,  p.  314,  PL  in.     (C.  affinis.) 

1819.  CLOQUET,  H.    Diet.  Sci.  Nat.,  Vol.  VIII,  p.  581, 

PL  xiv. 
1605.  CLUSIUS,    C.      Exoticorum    libri    decem,    p.    137. 

(C.  monstrosa.) 

1878.  COLENSO,   W.     Trans.    N.   Z.   Inst.,  Vol.   XI,  pp. 
298-300,   PL   xvn.     (Cal.   dasycaudatus.) 


1904. 
1905. 

1873. 

1852. 
1798 
1895. 
1904. 
1904. 
1900. 

1902. 
1803. 

1856. 

1865. 
1829. 


CoLLETT,-R.  Chr.  Videnskabs-Selskabs  Forh.,  No. 
4>  PP-  5-6.  [C.  (Bathyalopex)  mirabilis.] 

Rep.  on  Norwegian  Fishery  and  Marine 

Investigations.     Vol.   II,    No.   3,   p.   35,   PL   i. 
[Complete    account    of    C.    (Bathyalopex)    mi- 
rabilis.] 

COPE,  E.  D.  A  contribution  to  the  ichthyology  of 
Alaska.  Proc.  Amer.  Philos.  Soc.,  Vol.  XIII, 
No.  90,  pp.  24-32.  (C.  colliei.)  V.  also  Chi- 
maeroids, Skeleton,  and  Chimaeroids,  Fossil. 

COSTA,  O.  G.  Chimaera  (anat.),  Fauna  di  regno 
Napoli.  Pis.  i-vii.  (C.  monstrosa.) 

and  1817.  CUVIER.  Tableau  filementaire  and  in 
Regne  Animal,  Vol.  II,  pp.  382,  PL  cxin. 

DEAN,  BASHFORD.  Fishes,  Living  and  Fossil  (Mac- 
millan),  cf.  pp.  287-288. 

Jour.  Sci.  Coll.,  Tokyo,  Vol.  XIX,  Art. 

3,  pp.  10,  PL  i.     (C.  phantasma  and  C.  mitsukurii.) 

Jour.   Sci.   Coll.,  Tokyo,  Vol.  XIX,  Art. 


1901. 


1904. 


4.  pp.  23,  PL  ii.     (Rhinochimaera  pacifica.) 

DELFIN,  F.  T.  In  Catalogo  de  los  Peces  de  Chile. 
Rev.  Chil.  Hist.  Nat,  Vol.  Ill  (1899),  i,  IV, 
1900.  (Cal.  callorhynchus  and  Cal.  argenteus.) 

Concordancia  de  Nombres  Vulgares  i 

Cientificos  de  los  Peces  de  Chile.  Abstract  in 
Riv.  Chil.  Hist.  Nat.,  Vol.  VI,  pp.  71-76. 

DONOVAN,  E.  Nat.  Hist.  Brit.  Fishes.  Rivington, 
London.  PL  cxi,  and  accompanying  descrip- 
tion. Reference  to  a  "C.  monstrosa"  which  had 
conspicuously  spotted  fins. 

DUMERIL,  A.  Ichthyologie  analytique.  Indicates 
Chimaera  near  Spatularia — a  hypostomate  chon- 
drostean  (gives  name  Chismopnes  to  Chimasra, 
Lophius,  Batistes,  etc.). 

Hist.  Nat.  des  Poissons.  I.  filasmobranches, 

pp.  663-697,  Pis.  (Atlas)  xin-xiv.  (Standard 
reference  to  Chimaeroids.) 

FABER,  F.  Naturgeschichte  der  Fische  Islands, 
p.  45.  Frankfurt.  (C.  monstrosa,  its  habits, 
food,  etc.) 

GAIMARD,  J.  P.  Voyage  en  Islande  et  au  Green- 
land. Zool.  PL  xx.  Figures  Chimaera  mon- 
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CARMAN,  S.  Proc.  N.  Eng.  Zool.  Club,  Vol.  II, 
pp.  75-77.  (Rhinochimaera  and  taxonomical  con- 
siderations.) 

.  The  Chimaeroids  (Chismopnea  Raf.  1815, 

Holocephala,  MiilL,  1824),  especially  Rhinochi- 
maera and  its  allies.  Bull.  Mus.  Comp.  Zool., 
Vol.  XLI,  pp.  243-272,  Pis.  i-xv. 


i6o 


LITERATURE   LIST. 


1901.  GEGENBAUR,  C.  Many  ref.  in  Vergl.  Anat.  der 
Wirbeltiere.  2  vols.  Engelman.  Vertebral  col- 
umn "even  in  many  points  in  a  less  differentiated 
condition"  than  sharks ;  the  chorda  is  of  uni- 
form thickness  through  the  centra ;  palato-quad- 
rate  fused  with  cranium ;  median  union  of  three 
rostral  cartilages  in  Chimaera  more  shark-like 
than  in  Callorhynchus ;  male  median  clasper 
a  new  structure ;  ventral  labial  cartilage  a 
"second  under  jaw"  (J.  Miiller)  ;  agrees  with 
Solger  that  the  position  of  spiracle  was  be- 
hind the  articulation  of  the  mandible;  no 
mesopterygium  (fused  with  propterygium,  as 
in  Cestracion)  ;  antero-lateral  clasper  de- 
rived from  a  radial  cartilage;  muscles  of 
shoulder  girdle  more  modified  than  in  sharks ; 
loss  of  myocommata;  flattened  cord,  like  cyclo- 
stomes ;  lateral  line  primitive,  with  open  canal ; 
simplest  acoustic  macula ;  grooved  nostril,  like 
dipnoan ;  teeth  reduced,  i.  e.,  dental  plates,  equiv- 
alent to  oblique  rows  of  separate  teeth,  and 
produced  by  "concrescence  of  numerous  simpler 
teeth ;"  appears  to  regard  the  few  turns  of  intes- 
tinal valve  as  ancestral  to  condition  of  Lepi- 
dosteus  and  Ceratodus ;  comments  on  hinder 
position  of  pori  abdominales. 
1620.  GESNER,  C.  De  Aquatilibus,  pp.  877  et  seq. 
1896.  GILBERT,  C.  H.  Ichthyological  collection  of  "Al- 
batross," 1891-92.  (C.  colliei.)  Rep.  U.  S. 
Comm.  of  Fisheries.  Vol.  for  1893.  Washing- 
ton, 1896,  p.  398. 

Fishes  obtained  by  steamer  "Albatross " 

in  St.  Catalina  Island,  Monterey  Bay,  and  vicin- 
ity. (C.  colliei.)  Rep.  U.  S.  Comm.  of  Fish- 
eries for  1898.  Washington,  1899,  p.  25. 

GILL,  TH.     Smithsonian  Misc.  Collections,  p.  63. 

— •    Cat.  of  Fishes  of  the  E.  Coast  of  N.  Am. 

Proc.  Acad.  Nat.  Sci.  Phila.,  pp.  1-63. 

—  Proc.  Acad.  Nat.  Sci.  Phila.,  p.  331.     [Hy- 


1899. 

1860. 
1861. 

1862. 
1872. 
1877. 
1882. 
1883. 
1894. 

1859. 
1894. 
1894. 
1896. 


drolagus  (=Chimaera)  colliei.] 

Arrangement   of   the   Families   of   Fishes. 


Smithsonian  Misc.  Collections,  pp.   i-xlvi :  1-49. 
Tr.  Phil.  Soc.  Washington,  Dec.  22,  p.   I. 


(C.  plumbea.) 
Bull.  U.  S.  Nat.  Mus.,  Bibliogr.  Fishes  Pac. 


Coast.     (C.  colliei.) 
Proc.  U.  S.  Nat.   Mus.,  Vol.  VI,  p.  254- 


(C.  abbreviata.) 

Mem.    Nat.    Acad.    Sc.,   Vol.    VI,    p.    130. 


(Chimaeridae  divided  into  Chimserinae  and  Har- 

riottinae.) 
GIRARD,  C.    Rep.  U.  S.  Pacific  R.  R.,  Fish,  p.  360. 

(C.  colliei.) 
GOODE  and  BEAN.     Oceanic  Ichthyology,  pp.  243- 

272,  PI.  xv. 
—    Proc.  U.    S.   Nat.   Mus.,  Vol.   XVII,  pp. 

471-473,  PI-  xix.     (Harriotta  raleighana.) 
GRIEG,   J.    A.     Ichthyologiske    Notiser.     Bergens 

Mus.  Aarbog  for  1894-95.     Bergen,  1896. 


1756.  GRONOVIUS,  L.  T.  Museum  Ichthyologicum  and  in 
Systema  Naturae.  (C.  monstrosa.) 

1763. Zoophylacium,  Pt.  I,  p.  32.  (Callo- 
rhynchus.) 

1854.  GRONOVIUS.  Gray's  Edition  of  Catalogue  Fishes, 
pp.  15-16.  (Callorhynchus  centrinus  and  C.  at- 
lanticus.) 

1763.  GUNNER.  Der  Trondhiemske  Selskabs  Skrifter, 
Vol.  II,  p.  270,  Pis.  v  and  vi. 

1870.  GUNTHER,  A.  Cat.  Fishes  in  British  Museum, 
Vol.  VIII,  p.  350. 

1880.  Introduction  to  the  Study  of  Fishes,  pp. 

348-350. 

1887.  Reference  to  very  young  specimens  of  C. 

monstrosa.  Challenger  Report,  Vol.  XXII,  pp. 
12-13. 

1840.  HOBSON.  Tasmanian  Jour.  Sci.,  Vol.  I.  (Cal. 
australis.) 

1872.  HUTTON,  F.  W.  Fishes  of  New  Zealand.  Co- 
lonial Museum  and  Geological  Survey.  Hughes, 
Wellington,  p.  74.  (Cal.  antarcticus.) 

1895.  HOLT,  E.  W.  L.,  and  CALDERWOOO,  W.  L.    Report 

on  the  rarer  fishes.  Survey  of  Fishing  Grounds, 
West  Coast  of  Ireland,  1890-91.  Scientific 
Trans.  Roy.  Dublin  Soc.,  Vol.  V,  Ser.  II,  Pt.  IX, 
pp.  361-524- 

1902.  JAEKEL,  O.  Reference  to  Chimaera  as  the  most 
primitive  Plagiostome  in  Ueber  verschiedene 
Wege  phylog.  Entwicklung.  Fischer,  Jena. 
Pp.  58.  (Ex.  V.  Internal.  Zool.  Cong.  Berlin, 
1901.) 

— .  JARDINE.     Naturalist's  Library.     Fishes,  Vol.   Ill, 
pp.  295-296.     (C.  monstrosa.) 

1896.  JORDAN,    D.    S.,    and    EVERMANN,    B.    W.    The 

Fishes  of  North  and   Middle  America,  Vol.   I, 

PP.  93-97- 
1883.  JORDAN,    D.    S.,    and    GILBERT,    C.    H.      Synopsis. 

P.  54- 

1900.  JORDAN,  D.   S.,  and   SNYDER,  J.   O.     Proc.   U.   S. 

Nat.  Mus.,  Vol.  XXIII,  pp.  338-339-  (C.  phan- 
tasma.) 

1901.  -    A  preliminary  check-list  of  the  fishes  of 

Japan.     Annot.  Zool.  Jap.,  Vol.  TH,  Pts.  II  and 
III,  pp.  3I-I59-    Tokyo. 

1904. On  the  species  of  White  Chimoera  from 

Japan.  Proc.  U.  S.  Nat.  Mus.,  Vol.  XXVII, 
pp.  223-226,  2  figs.  (C.  mitsukurii  Dean  MS.) 

1838-53.  KROYER,  H.    Danmarks  Fiske,  Vol.  Ill,  p.  783. 

1798-1803.  LACEPEDE.  Hist.  Nat.  d.  Poissons,  Vol.  I, 
p.  392,  PI.  xix. 

1825.  LATREILLE.  Uses  Acantherina  for  Chimrera,  a 
family  of  Chondropterygiens  with  fixed  gills. 
Families  naturelles  du  regne  animal. 

1839.  LAY  and  BENNETT,     v.  BENNETT. 

1851.  LEYDIG,  F.  Zur  Anat.  u.  Histol.  d.  Chimera  mon- 
strosa. Mill.  Arch.  f.  Anat.  u.  Phys.,  Vol. 
XVIII,  pp.  241-271. 

1881-90.  LILLJEBORC,  W.    Sveriges  fiskar,  Vols.  I-III. 


LITERATURE   LIST. 


161 


1754,   1755.  LiNNfe,  C.     Systema  Naturae:   various  edi- 
tions, cf.  esp.  Gmelin's.     (C.  monstrosa.) 
1883.  MACLEAY.    Fishes  of  Australia.     (Callorhynchus.) 
1877.  MALM,  A.   W.     Goteborgs  och  Bohuslans  fauna. 

Ryggradsdjuren.     Goteborg.     (C.  monstrosa.) 
1896.  MAZZA,   FELICE.     Note   anatomo-istologiche   sulla 
Chimaera    monstrosa    Linn.    Atti    Soc.    Ligust. 
Sc.  Nat.  e  Geogr.    Ann.  6,  Fasc.  4,  15  pp.,  PI.  I. 
1889.  MONTICELLI,   F.    S.     Reference   to   food   of   Chi- 
maera.    Atti  d.  reale  Ace.  Lincei,  Vol.    (4)   V, 
Sem.  i. 

1833.  MULLER,  J.     V.  Chimaeroids  Skeleton. 
1776.  MULLER,  O.     Prodr.   Zool.   dan.,   No.   320,   p.   38. 

(C.  monstrosa.) 

1832  and  1855.  NILSSON,  S.  Prodr.  ichth.  scand.,  p.  112, 
and  Skand.  faun.  Fisk,  p.  705.  (C.  mon- 
strosa.) 

1896.  OLSSON,  PETER.    Sur  Chimaera  monstrosa  et  ses 
parasites.     Mem.   Soc.  Zool.  France,  Vol.   IX, 
No.  s,  pp.  499-512. 
1812.  PENNANT,  T.    British   Zoology;   Fishes,  Vol.   Ill, 

P.  159- 

18G8.  POEY,   F.     Synopsis   Piscium   Cubensium,  p.   445. 
— .  PONTOPPIDAN.       Norges,     etc.       (Translation     of 
History  of  Norway,  Vol.   II,   p.   114,   PI.   xxi. 
(Reference  to  C.  monstrosa.) 

1815.  RAFINESQUE,  C.  S.     Analyse  de  la  Nature,  p.  92. 
(Adopts  Chismopnea  for  Chimaeroids  and  other 
groups.) 
1713.  RAY,  J.     Reference   in    Synopsis    Piscium,   p.   23. 

(C.  monstrosa.) 

1877.  REGIUS,   J.   F.   M.     Essai   sur  1'histoire   naturelle 
de    la     Provence   et   des   departements    circon- 
voisins.     I.  Partie,  Poissons,  p.  78.     Paris,  Bail- 
Here.      (C.   monstrosa.) 
1835.  RICHARDSON,  J.     Fauna  boreali-Americ.,  Vol.  Ill, 

p.  286.     (C.  colliei.) 
1810.  Risso,  A.    Ichthyol.     Nice,  p.  53. 
1826.  _     —  Hist.   nat.   Eur.   merid.,   Vol.   Ill,   p.    168. 

(C.  mediterranea.) 
1804.  SHAW,  G.    General  Zoology,  Vol.  V,  Pt.  2,  p.  365, 

PI.  CLVII.     (C.  monstrosa.) 

1898.  SMITT,  F.  A.  Poissons  de  1'Expedition  Scien- 
tifique  a  la  Terre  de  Feu,  etc.  Bihang  till  K. 
Svenska  Vet.  Akad.  Handlingar,  Vol.  XXIV, 
Afd.  IV,  No.  3,  pp.  1-30. 

1847.  TEMMINCK,  C.  J.,  and  SCHLEGEL,  H.  H.     Fauna 
Japonica,  p.  300,  PI.  cxxxn.     ("C.  monstrosa.") 
1877.  THACHER,  J.  K.     Reference  to  Chimaera  as  a  di- 
vergent form  of  shark,  whose  nearest  relative  is 
Cestracion.     Trans.  Conn.  Acad.,  p.  284. 
1762.  VULPECULA,  STROM.     Phys.  og  oeconom.  beskriv. 

overfogder.  Sondmor,  p.  289. 

1898.  WAITE,  E.  R.  Report  upon  trawling  operations 
off  the  coast  of  New  South  Wales,  between  the 
Manning  River  and  Jervis  Bay,  carried  on  by 
H.  M.  C.  S.  "Thetis."  N.  S.  Wales  Sea  Fish- 
eries, pp.  56-58.  (C.  ogilbyi.) 

1904.  WAITE,  E.  R.  Mem.  N.  S.  W.  Naturalists'  Club, 
No.  2,  p.  ii.  (C.  ogilbyi.) 


1899.  WAITE,  E.  R.  Scientific  results  of  the  trawling  ex- 
peditions of  H.  M.  C.  S.  "Thetis."  Introduction, 
and  Fishes.  Mem.  Austr.  Mus.,  Vol.  IV,  Pt.  I, 
pp.  48-51.  (C.  ogilbyi.) 

1904. Mem.  N.  S.  W.  Naturalists'  club,  No.  2, 

p.  11.  (C.  ogilbyi.) 

1685.  WILLOUGHBY.  Historia  piscium,  p.  57;  also  fig., 
copied  from  Clusius.  (C.  monstrosa.) 

1829.  YARRELL.  Reference  in  British  Fishes,  Vol.  II, 
_pp.  464-467.  (C.  monstrosa). 

1891.  WOODWARD,  A.  SMITH.    V.  Chimaeroids  Fossil. 

1887.  ZITTEL,  K.  V.    V.  Chimaeroids  Fossil. 

SKELETON.     EXTREMITIES. 

1833-44.  AGASSIZ,  L.  Reference  to  clasping  organs, 
cf.  Chimaeroids  General;  also,  1871,  in  Proc. 
Boston  Soc.  Nat.  Hist.,  Vol.  XIV,  p.  339. 

1897.  ALLIS,  E.  P.  The  morphology  of  the  petrosal 
bone  and  of  the  sphenoidal  region  of  the  skull 
of  Amia  calva.  Zool.  Bull.,  Vol.  I,  pp.  1-26. 

1899.  BRAUS,  H.  Beitrage  zur  Entwicklung  der  Mus- 
kulatur  und  des  peripheren  Nervensystems  der 
Selachier.  2  Theile.  Morph.  JB.,  Vol.  XXVII, 
3  u.  4,  Leipzig,  pp.  415-629. 

1901.  Die  Muskeln  und  Nerven  der  Ceratodus- 

Flosse.  Ein  Beitrag  zur  vergleichenden  Mor- 
phologic der  freien  Gliedmasse  bei  niederen 
Fischen  und  zur  Archiptergiumtheorie.  Semon's 
Zool.  Forschungsreisen  Austr.  Malay.  Archip., 
Vol.  I,  Lief.  3,  pp.  137-300.  (Deutsch.  med. 
nat.  Gesell.  Jena,  Vol.  IV.) 

1870.  COPE,  E.  D.  Contribution  to  the  Ichthyology  of 
the  Lesser  Antilles.  Amer.  Philos.  Soc.,  Vol. 
XIV,  pp.  445-463. 

1879.  DAVIDOFF,  M.     Beitr.   zur  vergl.   Anat.   der  hint. 

Gliedmassen  der  Fische.  Morph.  JB.,  Part  I, 
pp.  450-520,  Pis.  xxvm-xxxi. 

1883.  -  —  Part  III.  Ceratodus.  Morph.  JB.,  Vol. 
IX,  pp.  117-162,  PI.  vni.  (Chimxra  pelvic  girdle 
and  fin,  pp.  142-143.) 

1880.  DAVIS,  J.  W.     On  the  teleostean  affinities  of  the 

genus  Pleuracanthus.  Ann.  Mag.  Nat.  Hist., 
Ser.  5,  Vol.  V,  pp.  349-357- 

1856.  DUMERIL,  A.     Cf.  Chimaroids  General. 

1903.  FURBRINGER,  KARL.  Beitrage  zur  Kenntniss  des 
Visceralskelets  der  Selachier.  Morph.  JB.,  Vol. 
XXXI,  Heft  2  u.  3,  pp.  360-445  (and  Nachtrag, 
ibid.,  H.  4,  pp.  620-622). 

1904. Beitrage  zur  Morphologic  des  Skelets  der 

Dipnoer.  Semon's  Zool.  Forschungsreise,  p.  502. 
(Chimaeroids  stand  further  from  Prodipnoans 
than  Pleuracanthus.) 

1897.  FURBRINGER,  M.  Ueber  die  spino-occipitalen 
Nerven  der  Selachier  u.  Holocephalen  u.  ihre 
vergleichende  Morphologic.  Festschr.  f.  Gegen- 
baur,  Vol.  Ill,  pp.  347-788.  Reference  to  Ex- 
tremitatentheorie.  Pp.  728  et  seq.  Reference 
to  lip  cartilages  (fusion  of  ventral  labial  carti- 
lage of  Callorhynchus  secondary),  p.  434. 


l62 


LITERATURE   LIST. 


1888.  GADOW,  HANS.  Modifications  of  the  first  and  sec- 
ond visceral  arches,  with  especial  reference  to 
the  homologies  of  the  auditory  ossicles.  Phil. 
Trans.,  Vol.  CLXXIX,  pp.  451-485,  Pis.  LXXI- 
LXXIV. 

1877.  CARMAN,  S.     On  the  pelvis  and  external  sexual 

organs  of  selachians.     Proc.   Boston   Soc.   Nat. 

Hist.,  Vol.   XIX.      Reference  to    Chimaeroids, 

pp.  198-201. 
1865.  GEGENBAUR,  C.     Ueber  den  Brustgurtel  und  die 

Brustflosse  der  Fische.     Jen.  Zeitschr.,  Vol.  II, 

pp.  121-125. 

1869.  U.  d.  Skelet  d.  Gliedmassen  d.  Wirbeltiere 

im    Allgemeinen    u.    d.    Hintergliedmassen    d. 
Selachier  insbesondere.     Ibid.,  Vol.  V,  pp.  397- 


1870. 


1872. 


447- 

—  t).  d.  Modificationen  des  Skelets  der  Hin- 
tergliedmassen d.  Mannchen  d.  Selachier  u.  Chi- 
maeren.    Ibid.,  pp.  448-458,  fig.     (Derives  antero- 
ventral  clasper  from  fin  skeleton.) 
Reference   in   Das   Kopfskelet   der    Sela- 


chier. 


1904.  GOODRICH,  E.  S.     On  the  dermal  fin  rays  of  fishes, 

living  and  extinct.     Quart.  Jour.  Micr.  Sci.,  N. 

S.,  Vol.   XLVII,  pp.  465-522,   Pis.  vii,  6  figs. 

(Reference  to  Chimaeroids.) 
1904.  GREGORY,  W.  K.    Reference  to  the  relations  of  the 

anterior  visceral  arches  in  Chimaera.    Biol.  Bull., 

Vol.  VII,  pp.  54-69,  figs. 
1879-82.  HASSE,   C.     Das   natiirl.    System   d.    Elasmo- 

branchier.     Jena,  p.  37. 
1887.  HowES,  G.  B.     On  the  skeleton  and  affinities  of 

the  paired  fins  of  Ceratodus,  with  observations 

upon  those  of  Elasmobranchii.     Proc.  Zool.  Soc. 

Lond.,  pp.  3-26. 

1890.  -    —    Observations  on  the  pectoral  fin  skeleton 

of  the  living  batoid  fishes,  and  of  the  extinct 
genus  Squaloraja,  with  especial  reference  to  the 
affinities  of  the  same.  Proc.  Zool.  Soc.  Lond., 
pp.  675-688. 

1891.  On    the    affinities,    interrelationships,    and 

systematic     position     of     the     Marsipobranchii. 
Proc.  and  Trans.  Liverpool  Biol.  Soc.,  Vol.  VI, 
pp.  122-147.     (Figures  labial  cartilages  of  Chi- 
maeroids   (Callorhynchus)    and   compares   them 
to  those  of  Myxinoids.) 

1902.  In  address  before  the  Brit.  Assn.  refers 

to  chordal  type  of  skel.   in   Chirmera.     Nature, 

Sept.  25,  p.  526- 
1901.  HUBER,  O.     Die  Kopulationsglieder  der  Selachier. 

Zeitschr.  f.  Wiss.  Zool.,  Vol.  LXX,  p.  87. 
1876.  HUBRECHT,  A.  A.  W.     Die  Ordnungen  d.  Fische. 

Bronn's    Klassen   u.    Ordnungen.     Liefg.    I-IV, 

Leipzig. 
1876-78.  Fins  of  Chimaera.     Bronn's  Klassen  u. 

Ordnungen,  Vol.  VI,  I.  Abth.,  p.  22,  Taf.  xxvin, 

Reference  to  horn   fibers  not  confirmed  by   P. 

Mayer. 


1877.  HUBRECHT,  A.  A.  W.  Beitrage  zur  Kenntniss 
des  Kopfskelets  der  Holocephalen.  Niederl. 
Arch.  f.  Zool.,  Vol.  Ill,  pp.  255-276. 

1877.  Notiz  iiber  einige  Untersuchungen  am 

Kopfskelet  der  Holocephalen.  Morph.  JB.,  Vol. 
Ill,  pp.  280-282. 

1876.  HUXLEY,  T.  H.  Reference  to  Chimseroid  fin. 
Proc.  Zool.  Soc.  Lond.,  pp.  52-53-  Cf.  also  his 
Comparative  Anatomy  of  the  Vertebrate  Animals. 

1899.  JAEKEL,  O.  Organisation  d.  Petalodonten.  Zeit- 
schr. deutsch.  geolog.  Gesell.,  Vol.  LI,  Heft  2, 
pp.  256-298. 

1897-99.  JAQUET,  MAURICE.  Contribution  a  1'anatomie 
comparee  des  systemes  squelettaire  et  muscu- 
laire  de  Chimaera  colliei,  Callorhynchus  antarc- 
ticus,  Spinax  niger,  Protopterus  annectans,  Cera- 
todus forsteri  et  Axolotl.  Arch.  Sci.  Med.  Bu- 
carest,  Vol.  II,  pp.  174-206;  Vol.  Ill,  pp.  300- 
340;  Vol.  IV,  pp.  189-225,  241-273. 

1898.  JUNGERSEN,  H.   F.  G.    Reference   to   Chimaeroid 

claspers.     Anat.  Anz.,  Vol.  XIV,  pp.  498-5*3- 

1899.  .    On  the  appendices  genitales  in  the  Green- 
land    shark,     Somniosus     microcephalus     (Bl. 
Schn.)    and   other   selachians.      Danish   Ingulf. 
Expedition,  Vol.  II,  pp.  88,  Pis.  v.     Reference 
to  Chimaera,  pp.  18,  20,  21,  76,  77,  83. 

1893.  KLAATSCH,  H.  Beitr.  zur  vergl.  Anat.  der  Wirbel- 
saule.  I.  Morph.  JB.,  Vol.  XIX,  pp.  649-680. 
General  reference  to  Chimaera,  pp.  666-670. 

1859.  KOLUKER,  A.  On  the  structure  of  the  chorda  dor- 
salis  of  the  Plagiostomes  and  some  other  fishes, 
and  on  the  relation  of  the  proper  sheath  to  the 
development  of  the  vertebrae.  Proc.  Roy.  Soc. 
Lond.,  Vol.  X,  pp.  214-222. 

1887.  LwoFF,  B.  Vergleichend-anatomische  Studien 
iiber  die  Chorda  und  die  Chordascheide.  Bull. 
Soc.  Imp.  Naturalistes  de  Moscou,  No.  2,  Pis. 
iv,  pp.  442-482. 

1879.  METSCHNIKOFF,  OLGA.  Reference  to  girdles  of 
Chimsera  monstrosa  in  Zeit.  f.  wiss.  Zool.,  Vol. 
XXXIII,  pp.  425,  428-430,  436,  PI.  xxiv. 

1886.  MEYER,  P.  Reference  to  vertebral  characters  of 
Chimaera.  MT.  Stat.  Neap.,  Vol.  VI,  pp.  265-270. 

1879.  MIVART,  S.  G.  Notes  on  the  fins  of  elasmo- 
branchs,  with  considerations  on  the  nature  and 
homologies  of  vertebrate  limbs.  Trans.  Zool. 
Soc.  Lond.,  Vol.  X,  pp.  439-484,  and  abstr.,  1878, 
Trans.  Zool.  Soc.,  pp.  116-120. 

1834.  MULLER,  J.  Summarizes  characters  of  Chimxroid. 
Abh.  Akad.  Berl.,  p.  74;  note  also  pp.  131, 141, 149, 
structure  of  cartilage,  vertebral  arches,  anterior 
condylar  facets.  Also  1838,  p.  238,  labial  carti- 
lages ;  pp.  197-202  (variable)  ;  quadrate  fusion, 
pp.  200-202,  221;  dental  plates,  p.  200;  skull  and 
suspensorium,  pp.  217-223;  gills,  pp.  217,  220; 
snout  cartilages,  pp.  229,  230,  233;  nasal  cap- 
sules, pp.  235,  236. 

1886.  PARKER,  T.  J.  On  the  claspers  of  Callorhynchus. 
Nature,  Vol.  XXXIX,  p.  635. 


LITERATURE   LIST. 


i63 


1897.  PARKER  and  HASWELL.  Reference  in  Textbook  of 
Zoology  (Macmillan),  Vol.  II,  pp.  173-183,  to 
pharyngohyal  of  second  arch  ("represents  hyo- 
mandibular  of  shark")  ;  halves  of  pelvic  arch 
separate  (joined  by  ligament  only)  ;  calcified 
ring-vertebrae  in  Chimaera ;  fused  pterygiophores 
in  dorsal. 

1883.  PARKER,  W.  K.  On  the  skeleton  of  the  marsipo- 
branch  fishes.  Phil.  Trans.  Roy.  Soc.  Refer- 
ence to  Chimaera,  pp.  450-451. 

1902.  PRINCE,  E.   E.     Reference  to  fin  of  Chimaera  in 

paper  on  Lamna  in  Supp.  to  32d  Annual  Rep.  of 
Dept.  of  Marine  Fisheries.  Ottawa,  1901. 

1897.  RABL,  C.  Theorie  des  Mesoderms.  Engelmann, 
Leipzig,  p.  299.  (Accepts  Chimaeroids  and  No- 
tidanus  as  phylogenetically  older  sharks.) 

1901.  — •  Reference  to  fins  of  Chimaera  as  indicating 

little  or  no  tendency  for  fusion  of  radials 
around  metapterygium.  Zeit.  f.  wiss.  Zool.,  Vol. 
LXX,  pp.  479,  482-483,  524,  525,  S3L  Reference 
to  vertebral  column  in  Chimaeroids,  p.  454. 

1892.  REIS,  O.  M.  Reference  to  skel.  characters,  "cen- 
tra," claspers,  in  O.  d.  Kopfstacheln  b.  Menas- 
pis  armata  Ewald.  Miinchen,  Kutzner. 

1.1!)5.  On  the  structure  of  the  frontal  spine  and 

the  rostro-labial  cartilages  of  Squaloraja  and 
Chimaera.  Geol.  Mag.,  Decade  IV,  Vol.  II,  pp. 
385-391,  PI.  xn. 

1897.  REYNOLDS,  S.  H.    The  vertebrate  skeleton.     Cam- 

bridge. 

1887.  RIESS,  J.  Reference  to  histol.  structure  of  clasp- 
ers of  Chimaera.  Palaeontographica,  Vol. 
XXXIV,  p.  17,  PL  H,  fig.  12. 

1904.  SABATIER,  A.  Sur  les  mains  scapulaires  et  pel- 
viennes  des  Poissons  holocephales  et  chez  les 
dipneustes.  C.  R.  Acad.  Sci.  Paris,  Vol. 
CXXXVIII,  pp.  249-252. 

1901.  SCHAFFER,  JOSEF.  Ueber  den  feineren  Bau  und 
die  Entwicklung  des  Knorpelgewebes  und  iiber 
verwandte  Formen  der  Stutzsubstanz.  Zeit.  f. 
wiss.  Zool.,  Vol.  LXX,  pp.  109-170. 

1903.  SCHAUINSLAND,   H.     Beitragc   zur   Entwicklungs- 

geschichte  und  Anatomie  der  Wirbelthiere. 
Zoologica,  Vol.  XVI,  Heft  39,  pp.  1-98. 

1904.  Reference   to   vertebral    column    of    Chi- 
maera in   O.   Hertwig"s   Handbuch   d.   Entwick- 
lungsgeschichte  d.  Wirbeltiere. 

1817.  SCHULTZE.  Nonnulla  de  primordiis  systematis 
ossium  et  de  evolutione  spinae  dorsi  in  animali- 
bus.  Merkel's  Archiv,  Vol.  IV,  p.  329.  Refers 
to  vertebrae  of  Chimaera  as  a  higher  "  Bildung- 
stufe  "  than  chordal.  500  rings  present. 

187G.  SOLGER,  B.  (Chimaera  monstrosa.  On  two  hith- 
erto undescribed  cartilages  in  the  visceral  skele- 
ton.) Morph.  JB.,  Vol.  I,  Heft  I,  pp.  219-221. 

MUSCLES,   INTEGUMENT,   AND   TEETH. 

1898.  ALLIS,  E.  P.,  jr.     Muscles  et  Nerfs  chez  1'Amia 

calva.  Arch,  de  Zool.  Exp.  et  Gen.,  3e  serie, 
Vol.  VI,  pp.  63-00. 


1900.  CORNING,  H.  K.  Ueber  die  vergleichende  Anato- 
mie der  Augenmuskulatur.  Morph.  JB.,  Vol. 
XXIX,  i,  pp.  94-140.  Refers  to  origin  of  rectus 
internus,  and  to  course  of  oculomotor.  Former 
resembles  condition  in  Petromyzon,  and,  accord- 
ing to  Allis  and  Gegenbaur,  is  primitive — their 
view  not  accepted  by  Corning. 

1852.  COSTA,  O.  G.     V.  Chimaeroids  General. 

1894.  DEAN,  BASHFORD.    V.  Chimaeroids  General. 
1904.  — — —    Notes  on  the  anatomy  of  Rhinochimaera 

in  Jour.  Sci.  Col.  Tokyo,  Art.  4,  pp.  23,  Pis.  II. 

1903.  FURBRINGER,   K.     Reference  to  musculi  levatores 

anguli  oris  in  Chimaera  as  constrictors,  thus  con- 
firming Vetter  as  to  their  primitive  nature. 
Morph.  JB.,  Vol.  XXXI,  H.  2  u.  3,  p.  387. 
1897.  FURBRINGER,  M.  Ueber  spino-occipitalen  Nerven 
der  Selachier  u.  Holocephalen  u.  ihre  verglei- 
chende Morphologic.  Leipzig,  Gegenbaur  Fest- 
schrift, Vol.  Ill,  pp.  347-788. 

1904.  GARMAN,  S.     V.  Chimaeroids  General. 

1870.  GUNTHER,  A.  Catalogue  of  Fishes  in  the  British 
Museum,  Vol.  VIII.  Reference  to  dorsal  row 
of  scales  in  Chimaera  and  in  .Scyllium,  p.  403. 

1873.  HEINCKE,  FR.  Untersuchungen  iiber  die  Zahne 
niederer  Wirbelthiere.  Zeit.  f.  wiss.  Zool.,  Vol. 
XXIII,  pp.  495-591- 

1897-99.  JAQUET,  M.    V.  Chimaeroids,  Skeleton. 

1886.  MEYER,  P.  Reference  to  dermal  denticle  ridges  in 
sharks,  which  appear  closely  akin  to  those  of 
Chimaera.  MT.  Stat.  Neap.,  Vol.  VI. 

1840.  OWEN,  R.  Odontography,  Vol.  I.  Reference  to 
Chimaeroid,  pp.  64-68.  Regards  dental  plates 
as  "an  extreme  but  still  more  anomalous  modi- 
fication of  the  chondropterygious  type,"  "like 
Cestracion." 

1891.  POLLARD,  H.  P.  Anat.  Anz.,  Vol.  VI,  pp.  338-344. 
Reference  to  the  reduction  of  dermal  defenses 
in  Chimaeroids. 

1895.  REIS,    O.    M.      Illustrationen   zur    Kenntniss    des 

Skelets  von  Acanthodes  Bronni,  Agassiz.  AH. 
Senckenberg.  naturforsch.  Gesell.,  pp.  49-64,  PI. 
Reference  to  median  tooth  of  "Prognathodon- 
ten  Holocephalen,"  p.  51. 

189G.  Ueber  Acanthodes  Bronni,  Agassiz. 

Schwalbe's  Morph.  Arb.,  Vol.  VI,  pp.  143-220. 
Reference  to  levator  anguli  oris  as  also  closing 
mouth  (adductor  in  Chimaera) — similar  condi- 
tion to  Acanthodes,  spines  also  correspond  struc- 
turally, and  granular  calcification  of  cartilage 
(Ischyodus). 

1878.  VETTER,  B.  Z.  vergl.  Anat.  d.  Kiemen-  u.  Kiefer- 
musculatur  d.  Fische.  II.  Jen.  Zeitschr.,  Vol. 
XII,  pp.  431-450.  Accepts  fusion  of  palate  with 
skull.  Muscles  like  Heptanchus,  but  "  less  spe- 
cialized and  differentiated  than  in  any  one  of 
the  sharks  investigated,  a  state  indeed  which  in 
its  ground  plan  enables  us  to  reconstruct  hypo- 
thetically  the  comparative  estimate  of  the  latter." 


164 


LITERATURE  LIST. 


1886.  WORTMAN,  J.  S.  Teeth  of  the  Vertebrata.  Ref- 
erence in  vol.  from  Amer.  System  of  Dentistry, 
PP-  364-379. 

VISCERA,  CIRCULATORY. 

1886.  BEMMELEN,  J.  F.  VAN.  Reference  to  the  entire 
degeneration  of  the  hindmost  (sth)  gill  slit  in 
Chimaera.  MT.  Stat.  Neapel,  p.  171. 

1898.  BLES,  E.  J.  On  openings  in  wall  of  body-cavity 
of  Vertebrates.  Proc.  Roy.  Soc.  Lond.,  Jan.  13, 
Vol.  LXII,  pp.  232-247. 

—    The  correlated  distribution  of  abdominal 


1898. 

189T. 
1837. 

1839. 
1865. 

1884. 
1886. 
1890. 

1890. 

1891. 
1853. 
1879. 
1894. 

1895. 
1836. 


pores  and  nephrostomes  in  Fishes.    Jour.  Anat. 

and  Phys.,  Vol.  XXXII,  pp.  483-512. 
COLLINGE,    W.    E.     The    supra-renal    bodies    of 

Fishes.    Nat.  Sci.,  Vol.  X,  No.  63,  pp.  318-322. 
DUVERNOY,  M.     Sur  deux  bulbes  arteriels  faisant 

les  fonctions  de  cceurs  accessoires,  qui  se  voient 

dans  les  arteres  innominees  de  la  Chimere  arc- 

tique.     Annales    des    sciences    naturelles,    Vol. 

VIII,  pp.  35-41,  PI.  in,  fig.  2. 

Du  mecanisme  de  la  respiration  dans  les 

Poissons.     Paris.     Ibid.,  Vol.   XII,   p.   27,    Pis. 

V-VI. 

GEGENBAUR,  C.  Zur  vergleichenden  Anat.  des 
Herzens.  I.  Ueber  den  Bulbus  arteriosus  der 
Fische.  Jen.  Zeitschr.,  Vol.  II,  pp.  365-385. 

Ueber    d.    Abdominalporen    der    Fische. 

Morph.  JB.,  Vol.  X,  pp.  462-464. 

Ueber    d.    Conus    arteriosus    d.    Fische. 


Morph.  JB.,  Vol.  XIII,  pp.  405. 

HOWES,  G.  B.  Reference  to  rudiment  of  vesicula 
seminalis  in  female  Chimaera  (re  cloacal  caecum). 
Linn.  Soc.  Jour.,  Vol.  XXIII,  p.  405. 

Reference  to  Chimaeroids  in  visceral  anat- 
omy of  Australian  Torpedo  (Hypnos  subni- 
grum).  Proc.  Zool.  Soc.  Lond.,  No.  XLV, 
pp.  669-674. 

Reference   to   Holocephala   having    (with 


sharks)  nephrochidic  characters.  Cardiff  Meet- 
ing of  British  Ass'n. 

HYRTL,  J.  Reference  to  viscera,  especially  repro- 
ductive organs,  of  Chimaera.  SB.  Akad.  Wien, 
Vol.  XI,  p.  1085  et  seq. 

LANKESTER,  E.  R.  On  the  hearts  of  Ceratoclus, 
Protopterus  u.  Chimaera.  Proc.  Zool.  Soc.  Lond., 
Vol.  X,  pp.  493-506,  Pis.  n. 

MAZZA,  F.,  and  PERUGIA,  A.  Sulla  glandula  digiti- 
forme  (Leydig)  nclla  Chimaera  monstrosa  Linn. 
Atti  Soc.  Lig.  di  Sc.  Nat.,  Anno  V,  fasc.  II. 
Genoa. 

MAZZA,  F.  Note  anatomo-istologiche  sulla  Chi- 
maera monstrosa.  Atti  Soc.  Lig.  di  Sc.  Nat., 
Vol.  VI,  pp.  15,  PI.  xn.  Reference  to  spermato- 
genesis. 

MULLER,  J.  Vergl.  Anat.  d.  Myxinoiden.  AH. 
Akad.  Berlin.  Reference  to  bulbus,  p.  193;  circ. 
cephal.,  pp.  196-289;  gill  ves.,  p.  196;  pseudo- 
branch  absent,  p.  253. 


1S96.  OPPEL,   A.     Reference   to   stomach,   in   Lehrb.   d. 

vergl.  mikr.  Anat.  d.  Wirbelth.,  Vol.  II.     Jena, 

Fischer. 
1898.  Verdauungs-Apparat ;      Mundhohle     mit 

Zunge ;      Speicheldriisen ;      Schlund ;      Magen ; 

Darm ;     Brunnersche     Driisen ;     Bauchspeichel- 

driise ;    Leber.      III.    Ergebnisse    der    Anat.    u. 

Entwickelungsgeschichte,  Vol.  VIII,  pp.  124-100. 
1867.  PANCERI,    P.     Circa    particolaria    appendici    delle 

branche  della  Cephaloptera  giorna.    R.  Accad.  d. 

Sci.  d.  Napoli,  pp.  3-7. 
1898.  PARKER  and  HASWELL.    Reference  in  Textbook  of 

Zoology (Macmillan), Vol.  II,  pp.  173-183,  to  gills, 

testes,  spermatophores,  vestigial  Miillerian  duct. 

1898.  REDEKE,  H.   C.     Onderzoekingen   betreffende   het 

Urogenitaalsysteem   der    Selachicrs   en   Holoce- 
phalen.     Helder,  C.  de  Boer  Tt.,  pp.  85,  Pis.  n. 

1899.  Kleine    Beitrage    zur   Anatomic   der    Pla- 

giostomen.     Tijds.   Ned.   Dierk.  Ver.    (2),  Vol. 
VI,  pp.  II9-I35- 

1894.  SPENCER,  B.  Contributions  to  our  knowledge  of 
Ceratodus.  PI.  I.  The  blood  vessels.  Macleay 
Memorial  Volume,  pp.  1-34,  Pis.  v.  Reference 
to  opercular  gill  of  Chimaeroids,  cartoids,  intra- 
intestinal  vein. 

1898.  D.  Bau  der  Lungen  v.  Ceratodus  u. 

Protopterus.  DS.  Med.  Naturw.  Gesell.,  4, 8  pp. 

1903.  STEPHAN,  P.  L'evolution  des  corpuscles  centraux 
dans  la  spermatogenese  de  Chimaera  monstrosa. 
C.  R.  Soc.  Biol.  Paris,  Vol.  LV,  pp.  265-267. 

1876-77.  STOHR.  Ueber  d.  Conus  arteriosus  d.  Selach., 
Chim.  u.  Ganoiden.  Morph.  JB.,  Vol.  II,  pp. 
197-228. 

1902.  STUDNICKA,  F.  K.  Ueber  das  Epithel  der  Mund- 
hohle von  Chimaera  monstrosa  mit  besondcrer 
Berikksichtigung  der  Lymphbahnen  derselben. 
Bibliogr.  Anat.  Nancy,  Vol.  XI,  pp.  217-233,  5  figs. 

1874.  VETTER,  B.  Unt.  z.  vergleich.  Anat.  d.  Kiemen- 
u.  Kiefermusculatur  d.  Fische  (Elasmobranchii). 
Jen.  Zeit.  Nat.,  Vol.  IX,  pp.  405-456. 

NERVOUS  SYSTEM  AND  END  ORGANS. 

1897.  ALLIS,   E.    P.     The   morphology   of   the   petrosal 

bone  and  of  the  sphenoidal  region  of  the  skull 
of  Amia  calva.    Zool.  Bull.,  Vol.  I,  pp.  1-26. 

1898.  BRAUS,  H.     Cf.  Chimaeroids,  Skeleton. 

1838.  BRESCHET,  M.  G.  Recherches  anatomiques  et  phy- 
siologiques  sur  1'organe  de  1'oui'e  des  Poissons. 
Mem.  Acad.  Sci.  Inst.  France,  Vol.  V,  pp.  7°-73- 

1894.  BURCKHARDT,  R.  Bauplan  d.  Wirbelthiergehirns. 
Schwalbe's  Morph.  Arb.,  Vol.  IV,  pp.  131-150; 
V,  p.  137,  PI-  vin. 

1893.  Vergl.  Anat.  d.  Vorderhirns  bei  Fische. 

Anat.  Anz.,  Vol.  IX,  pp.  375-382. 

1901.  BURNE,  R.  H.  Note  on  the  innervation  of  the 
supraorbital  canal  in  the  catfish  (Chimaera  mon- 
strosa). Proc.  Zool.  Soc.  Lond.,  Vol.  I,  pp. 
184-187. 

1849.  BUSCH,  W.  De  Selachiorum  et  Ganoideorum  En- 
cephalo.  Inaug.  Dissert.  Berlin. 


LITERATURE   LIST. 


189G.  COLE,  F.  J.  The  cranial  nerves  of  Chimaera  mon- 
strosa.  Proc.  Roy.  Soc.  Edinb.,  Vol.  XXI, 
March,  pp.  49-50. 

1896.  —  —  On  the  sensory  and  ampullary  canals  of 
Chimaera.  Anat.  Anz.,  Vol.  XII,  No.  7,  pp. 
172-182. 

1890.  On  the  cranial  nerves  of  Chimaera  mon- 

strosa  Linn.,  with  a  discussion  of  the  lateral 
line  system  and  of  the  morphology  of  the  mem- 
brana  tympani.  Trans.  Roy.  Soc.  Edinb.,  Vol. 
XXXVIII,  part  3,  No.  19,  pp.  631-680. 

ISDN.  —  —  Structure  and  morphology  of  the  cra- 
nial nerves  and  lateral  sense  organs  of  fishes, 
with  special  reference  to  the  genus  Gadus. 
Trans.  Linn.  Soc.  Lend.,  (2)  Zool.,  Vol.  VII, 
pp.  115-221,  Pis.  in.  Reference  to  Chimaera. 

1898.  —  -  Reflexions  on  the  cranial  nerves  and  sense 
organs  of  fishes.  Trans.  Liverp.  Biol.  Soc.,  Vol. 
XII,  pp.  228-247.  Reference  to  Chimaera:  Cra- 
nial nerves  have,  except  in  one  case,  independent 
roots,  archaic,  perhaps  primitive ;  Chimaeroids 
less  divergent  skeletally  from  palaeozoic  ances- 
tors than  teleosts  from  theirs.  P.  244. 

1899. On  the  cranial  nerves  and  sense  organs 

of  fishes.  Anat.  Anz.,  Vol.  XVI,  No.  2,  pp.  40-48. 

1896.  COLLINGE,  W.  E.  On  the  sensory  and  ampullary 
canals  of  Chimaera.  (Abstr.)  Zool.  Anz.,  Vol. 
XIX,  No.  493,  p.  31.  Same  title:  Proc.  Zool. 
Soc.  Lond.,  Vol.  IV,  pp.  878,  888,  800. 

1892.  EWART,  J.  C.  The  lateral  sense  organs  of  elasmo- 
branch.  I :  The  sensory  canals  of  Laemargus. 
Edinb.  Roy.  Soc.,  July,  1891,  Vol.  XVII,  pp.  59- 
105.  Zool.  Anz.,  No.  387,  1892,  pp.  1-3. 

1896.  FURBRINGER,  M.  Ueber  die  spino-occipitalen  Ner- 
ven  der  Selachier  und  Holocephalen  und  ihre 
vergl.  Morphologic.  Festschr.  f.  C.  Gegenbaur, 
Vol.  Ill,  pp.  351-788. 

1888-89.  CARMAN,  S.  Lat.  line  of  selach.  and  holoce- 
phali.  Bull.  Mus.  Comp.  Zool.,  Harv.  Coll.,  Vol. 

XVII,  p.  57. 

1877.  HUBRECHT,  A.  A.  W.  Beitrag  zur  Kenntniss  des 
Kopfskelets  der  Holocephalen.  Niederl.  Archiv 
f.  Zool.,  Vol.  Ill,  pp.  255-276. 

1903.  JAEKEL,  O.     Reference  to  the  presence  of  an  epi- 

physeal  opening  in  the  cranium  of  Chimaera 
monstrosa.  SB.  Gesell.  Naturf.  Freunde  Ber- 
lin, pp.  35-36. 

1851.  LEYDIG,  F.  Zur  Anat.  u.  Histol.  d.  Chimaera  mon- 
strosa. Mill.  Arch.  f.  Anat.  u.  Physiol.,  Vol. 

XVIII,  pp.  241-271. 

1864.  MAYER,  F.  J.  C.  Reference  to  Chim.  in  Ueber  den 
Bau  des  Gehirns  Fische  in  Beziehung  auf  eine 
darauf  gegriindete  Eintheilung  dieser  Thier- 
klasse.  Nova  Acta  Acad.  Cass.  Leop.  Nat.  Cu- 
rios., Vol.  XXX,  AH.  VI. 

1904.  MERRITT,  O.  A.    The  theory  of  nerve  components. 

J.  Anat.  and  Phys.,  Vol.  XXXIX.  Reference  to 
Chimaera,  p.  207. 


1870.  MIKLUCHO-MACLAY   (and  GEGENBAUR,  C.).     Note 

on   brain   of   Chimaera.     Jen.   Zeitschr.,  Vol.   V, 

p.  132. 
1851.  MULLER,  H.     Ueber  d.  nervosen  Follikel-Apparat 

d.   Zittcrrochcn   u.   d.   sogen.   Schleimkanale   der 

Knorpel-Fische.     Erl.  Verh.  Phys.-Med.  Gesell. 

Wiirzburg,  Vol.  II,  No.  10,  pp.  134-150. 
1842.  MULLER,  J.     Remarks   upon  Valentin's   paper  on 

the  nerves  and  heart  of  Chimaera.     Bericht  iiber 
— die  Fortschritte   der   vergleichenden   Anat.    der 

Wirbelthiere  im  Jahre  (1842).     Archiv  f.  Anat., 

1843,  p.  253. 
1846.  Reference    to    Chimaera    in    Ueber    den 

Bau  und  die  Grenzen  der  Ganoiden  und  iiber  das 

natiirliche  System  der  Fische.     Abhandl.  Akad. 

Wiss.  Berlin,  pp.  117-216. 

1898.  PARKER  and  HASWELL.    Reference  in  Textbook  of 

Zoology  (Macmillan),  Vol.  II,  pp.  173-183,  to 
brain  of  Callorhynchus  as  unlike  Scyllium,  but 
having  fairly  close  resemblance  to  Scymnus. 

1901.  RABL,  C.  Reference  to  Fiirbringer's  work  on  cra- 
nial nerves  of  Chimaeroids.  Zeit.  wiss.  Zool., 
Vol.  LXX,  p.  529. 

1881-84.  RETZIUS,  G.  Das  Gehororgan  d.  Wirbelthiere. 
Morph.-histol.  Studien.  2  Theile.  Stockholm, 
pp.  101-104. 

1897.  RUGE,  G.  Reference  to  distribution  of  facial 
nerve  in  Chimaeroids.  Festschr.  f.  Gegenbaur, 
Vol.  Ill,  pp.  207,  213,  250-254. 

1879.  SCHWALBE.     Reference  to  nerves  of  Chimaera  in 

Das  Ganglion  Oculomotorii.  Jen.  Zeitschr.,  Vol. 
XIII,  p.  173- 

1880.  SOLGER,    B.     Reference    to    histology    of    sensory 

canals  in  Chimaera  in  Neue  Untersuchungen  zur 

Anatomic  der  Seitenorgane  der  Fische.    Archiv 

mikr.  Anat.,  Vol.  XVII,  p.  95- 
1889.  Mauthner'sche  Fasern  bei  Chimaera.  Morph. 

JB.,  Vol.  XV,  pp.  322-324,  PI.  xxvn. 
1849.  STANNIUS,    H.     Reference    to    Chimaera    in    Das 

periph.  Nervensystem.     Rostock. 
1854.  Handbuch  der  Anatomic  der  Wirbelthiere. 

Berlin. 

1895.  STUDNICKA,   F.   K.     Beitrage   zur   Anatomie   und 

Entwickelungsgeschichte  des  Vorderhirns  der 
Cranioten.  SB.  bohm.  Gesell.  Wiss.,  pp.  1-42. 

1896.  -    —     Same  title,  pp.  1-32. 

1899.  Ueber  das   Ependym   des   Centralnerven- 

systems    der   Wirbelthiere.     SB.    bohm.    Gesell. 
Wiss.,  pp.  1-7. 

1900.  Zur    Kenntniss    der    Parietalorgane    und 

der  sog.   Paraphyse  der  niederen  Wirbelthiere. 
VH.  d.  Anat.  Gesell.,  pp.  101-110. 

Ueber  das  Ependym  des   Centralnerven- 


1900. 


systems  der  Wirbelthiere.  SB.  bohm.  Gesell. 
Wiss.,  No.  45,  pp.  7. 

1900.  Der  "Reissnersche  Faden"  aus  dem  Cen- 

tralkanal  des  Riickenmarkes  und  sein  Verhalten 
in  dem  Ventriculus  (Sinus)  terminalis.  Ibid., 
No.  36,  10  pp. 


1 66 


LITERATURE  LIST. 


1842.  VALENTIN.     Ueber     das     centrale     Nervensystem 

und  die  Nebenherzen  der  Chimaera  monstrosa. 

Miiller's  Archiv  f.  Anat,  pp.  25-45. 
1877.  WILDER,    B.    G.     Brain    of    Chimaera    monstrosa. 

Proc.  Phil.  Acad.  Sci.,  May,  pp.  219-250. 
1898.  Reference  to  olfactory  portion  of  brain  of 

Chimsera.     Science,  N.  S.,  Vol.  VII,  pp.  150-152. 

EMBRYOLOGY. 
(Mainly  references  to  egg  capsules.) 

1890.  ALCOCK,  A.     Cf.  Wood-Mason  and  Alcock. 
1892.  Reference    to    egg    capsule    of    Chimaera 

monstrosa  dredged  at  410  fathoms  off  the  Coro- 

mandel  coast.     Indian  Marine  Survey. 
1869.  BESSELS,     E.     Reference    to    egg    of    Ischyodus 

from  Jurassic  of  Wiirtemberg  in  Jahreshefte  d. 

Ver.  f.  vaterl.  Naturkunde  in  Wiirtt.,  Vol.  XXV, 

p.  152,  PL  in. 
1875.  COLLETT,  R.     Norges  Fiske.     Tillaegshefte  til  Vi- 

denskabs  Selsk.  Forhandl.  for  1874.    Christ.,  1875. 

Figures  egg  of  Chimaera. 
1871.  CUNNINGHAM,  R.   O.     Notes   on   Callorhynchus : 

egg  figured.     Nat.  Hist,  of  Strait  of  Magellan 

(of  the  "Nassau"),  p.  340. 
1897.  DEAN,  B.,  CALKINS,  G.  N.,  HARRINGTON,  N.  R., 

and  GRIFFIN,  B.   B.     The  Columbia  University 

Zoological   Expedition   of    1896.     With   a   brief 

account    of    the    work    of    collecting    in    Puget 

Sound  and  on  the  Pacific  Coast.    Trans.  N.  Y. 

Acad.  Sci.,  Vol.  XVI,  pp.  33-42. 
DEAN,  BASHFORD.     On  the  embryology  and  phy- 

logeny    of    Chimaera.     Abstr.    of    paper    before 

Amer.    Morph.    Soc.     Science,   N.    S.,   Vol.   XI, 

pp.  169-170. 
—    The  early  development  of  sharks  from  a 

comparative    standpoint.      Science,    N.    S.,   Vol. 

XV,  No.  381,  p.  626. 

The     development     of     Chimsera    colliei. 


1900. 

1902. 

1903. 
1904. 

1904. 
1904. 
1904. 

1904. 
1904. 

1865. 


Biol.  Bui.,  Vol.  IV,  pp.  270-286,  figs. 

Reference  to  capsule  of  Chimaera  mitsu- 


kurii.    Jour.  Sci.  Coll.  Tokyo,  Vol.  XIX,  Art.  3, 
pp.  6-7,  PI.  i,  fig.  2. 

Reference   to  capsule  of   Chimasra  phan- 


tasma.    Jour.  Sci.  Coll.  Tokyo,  Vol.  XIX,  Art.  3, 
pp.  5-6,  PI.  i,  fig.  4. 

Reference    to    capsule    of    Rhinochimasra 


pacifica.    Jour.  Sci.  Coll.  Tokyo,  Vol.  XIX,  Art. 
4,  pp.  18-19,  PI.  II. 

Evolution  in  a  determinate  line  as   illus- 


trated  by   the   egg   cases   of   Chimaeroid   fishes. 
Biol.  Bull.,  Vol.  VII,  pp.  105-112. 

The  egg  cases  of  Chimasroid  fishes.    Am. 


Nat.,  Vol.  XXXVIII,  pp.  486-487. 

L'osuf  de   Chimaera   colliei  et   1'adaptation 


de  sa  capsule.     C.   R.  de  la  Soc.  de  Biologic 
(Seance  du  2  Juillet),  Vol.  LVII,  p.  14- 
DUMERIL,    A.     Reference    to    capsule    of    Callo- 
rhynchus in  Elasmobranches,  Vol.  I,  p.  683,  and 
Atlas,  PI.  vin,  figs.  6,  7,  and  8. 


1899. 

1905. 
189C. 

1899. 
1880. 

18S7. 


1889. 


GARMAN,  S.  Report  on  an  expedition  off  the 
west  coast  of  Mexico.  Mem.  Mus.  Comp.  Zool., 
Vol.  XXIV,  p.  20,  and  PI.  LXIV,  fig.  2.  Refer- 
ence to  capsule  of  "Callorhynchus  antarcticus.'' 

GILL,  THEO.  An  interesting  Cretaceous  Chimae- 
roid egg-case.  Science,  N.  S.,  Vol.  XXII,  pp. 
601-602. 

GRIEG,  J.  A.  Ichthyologiske  Notiser.  Bergens  Mu- 
seums Aarbog  for  1894-95.  Figures  imperfect 
capsule  of  C.  monstrosa. 

Similar  note.     Ibid,  for  1898. 

GUNTHER,  A.    Figure  of  capsule  of  Callorhynchus 

in  Study  of  Fishes,  p.  169. 

In  Challenger  Reports,  Vol.  XXII,  pp.  12- 

13,  reference  to  very  young  individuals  taken  by 
"Triton"   and   "Knight   Errant,"   and  comments 
on  the  precocious  appearance  of  claspers.     "No 
well-authenticated    egg    (of    Chimaera)    in    any 
collection." 

Deep-sea   trawling  cruise  off  the   S.   W. 


coast  of  Ireland.  Chimaera  "monstrosa"  egg  cap- 
sule 6f/2  inches  long  dredged  at  315  fathoms.  'No 
filaments  for  adhesion ;  they  would  probably  be 
useless  at  a  depth  where  the  water  is  probably 
quiet.  The  eggs  lie  on  the  ground  or  are  im- 
planted in  the  ooze  by  their  styliform  end.'  Ann. 
N.  H.  (6),  Vol.  IV,  pp.  415-417,  ng.  Refer- 
ence to  capsule  of  C.  phantasma,  but  without 
description  or  figure. 

1897.  HOWES,  G.  B.  Remarks  on  eggs  of  Bdellostoma 
and  Chimaera.  Linnaean  Soc.  (Exhibition  of 
above),  Feb.  4. 

1901.  JAEKEL,  O.  Notes  on  capsules  of  Chimaera,  Callo- 
rhynchus and  Ischyodus  (=Aletodus)  in 
Neues  JB.  f.  Mineral.,  Geol.  u.  Palaeont.,  Vol. 
XIV,  pp.  552-554.  P's.  xxn-xxiv,  and  figs.  3. 

1858.  LUTKEN,  C.  F.  Reference  to  capsule  of  Chimasra 
in  Nogle  Bemasrkninger  om  de  nordiske 
Aegaarter.  Vid.  Meddel.  fra  d.  naturh.  For., 
Nos.  5-7. 

1877.  MALM,  A.  W.  Similar  reference  in  Goteborgs 
och  Bohuslans  fauna.  Ryggradsdjuren.  Gote- 
borg. 

1895.  MAZZA,  F.     Reference  to  development  of  frontal 

organ  in  Chimaera  in  Atti  Soc.  ligus.  Sci.  nat., 
Vol.  VI,  p.  IS,  PL  xii. 

1842.  MULLER,  J.  Fig.  of  egg  capsule  of  Callorhynchus 
in  "Ueber  den  glatten  Hai."  SB.  Akad.  Berlin, 
PL  vi,  fig.  3.  (Still  the  best  figure  of  this  cap- 
sule!) 

1855.  NILSSON,  S.  Skandinavisk  fauna,  Vol.  IV,  Fis- 
karne.  Lund. 

1896.  OLSSON,  P.     Sur  Chimaera  monstrosa  et  ses  Para- 

sites. Mem.  Soc.  Zool.  France,  Vol.  IX,  No.  5, 
pp.  449-501.  (Figures  an  imperfect  egg  capsule.) 

1897.  PARKER    and    HASWELL.     Textbook    of    Zoology. 

Figures  capsule  of  Callorhynchus,  Vol.  II,  p.  182. 


LITERATURE   LIST. 


167 


1886.  RENAULT,  B.,  and  ZELLER,  R.  Reference  to  Fayo- 
lia  and  Palxoxyris  (Spirangium)  in  Comptes 
rendus  de  1'Academie  des  Sciences,  Vol.  CVII, 
p.  1022. 

1903.  SAUVAGE,  H.  E.  Reference  to  Jurassic  Spiran- 
gium in  Mem.  Real.  Acad.  Cienc.  Art.  de  Barce- 
lona, Vol.  IV,  pp.  6-7,  PL  i,  fig.  i. 

1903.  SCHAUINSLAND,  H.  Beitrage  zur  Entwicklungs- 
geschichte  und  Anatomie  der  Wirbelthiere.  I. 
Callorhynchus.  Zoologica,  Vol.  XVI,  Heft  39, 
pp.  1-98,  Pis.  xn-xxiv.  (Also  preliminary  notice 
in  VH.  V.,  internat.  Zool.  Congr.  Berlin,  pp. 
658-659.) 

1903.  STEPHAN,  P.  L'evolution  des  Corpuscles  Cen- 
traux  dans  la  Spermatogenese  de  Chimaera  mon- 
strosa.  Comptes  rendus  des  seances  de  la  Re- 
union Biologique  de  Marseille,  Feb.  17,  pp.  1-3. 
Also  in  C.  R.  Soc.  Biol.  Paris,  Vol.  LV,  pp. 
265-267. 

1882.  VAILLANT,  L.  "Travaillgur"  finds  young  Chi- 
maera (130  mm.)  with  fragments  of  egg  case  in 
Gulf  of  Gascony. 

1901.  VAVRA.  Comments  upon  and  figures  egg  capsule 
of  Callorhynchus  in  Vesmir,  pp.  184-185. 

1891.  WOOD-MASON,  J.,  and  ALCOCK,  A.  Reference  to 
capsule  of  "  PCallorhynchus  "  (  =  ?Harriotta 
indica)  in  Ann.  Mag.  Nat.  Hist.,  6  ser.,  Vol. 
VIII,  pp.  21-22,  fig.  Specific  name  by  (1899) 
Garman,  S.,  in  Mem.  Mus.  Comp.  Zool.,  Vol. 
XXIV,  p.  21. 

FOSSIL  CHIM/EROIDS. 

[In  preparing  the  present  summary  the  author  acknowledges 
his  indebtedness  to  Smith  Woodward's  Catalogue  of  Fossil 
Fishes  in  the  British  Museum,  Vol.  II.] 

AGASSIZ,  L. 

1833-44.  Recherches  sur  les  poissons  fossiles. 

Reference  to  Spinacorhinus  (=Squaloraja). 
Feuill.,  1837,  p.  94,  and  Vol.  Ill,  Pis.  XLII,  XLIII, 
and  1834,  Vol.  Ill,  p.  381. 

Reference  to  Chimxra  (Ischyodon)  johnsonii,  p. 
344,  PI.  XL  c,  fig.  22;  also  Chimxra  (Ischyo- 
don) egertoni,  Vol.  Ill,  p.  340,  PI.  XL  c,  figs. 

I-IO. 

Reference  to  Myriacanthus.    Ibid.,  p.  38,  PI.  vi,  and 

p.  39,  PI.  vni  a,  figs.  14,  15. 
Reference  to  Myriacanthus  granulatus.     Ibid.,  p. 

40,  PI.  vni  a,  fig.  16,  1837. 
Reference  to  Lcptacanthus  tenuispinus.     Ibid.,  p. 

27,  PI.  i,  figs.  12,  13. 
Reference  to  Spinacorhinus  polyspondylus.     Ibid., 

Pis.  XLII,  XLIII,  and  Feuil.,  p.  94,  1836. 
Reference  to  Lcptacanthus   (Ganodus),  Vol.  Ill, 

p.  27,   (in  part),  1837. 
Reference  to  Psittacodon  (Ganodus).     Ibid.,  1843, 

p.   340;    Psittacodon    (Edaphodon).     Ibid.,   340 

(in  part). 
Reference  to  Chimaera   (Ganodus)  owenii.     Ibid., 

p.  347,  PI.  XL,  figs.  6. 


AGASSIZ,  L. — (Continued.) 

Reference    to    Chimxra    (Ganodus)    colei.     Ibid. 

(ex  Buckland  MS.),  p.  346,  PI.  XL,  figs.  8-10. 
Reference  to  Chimaera  (Ischyodon)  tessoni.   Ibid., 

p.  342,  PI.  XL,  fig.  19. 
Reference  to   Chimaera    (Ischyodon)    beaumontii. 

Ibid.,  p.  346. 

Reference   to   Chimaera    (Ischyodon)    townsendii. 
Ibid.,  p.  343,  PI.  XL,  figs.  20-22 ;  PL  XL  c,  figs.  17, 
_i8._ 
Reference  to  Chimaera    (Ischyodon)   brevirostris. 

Ibid.,  p.  344  (name  only). 
Reference  to  Chimaera  ( Ischyodon )agassizii.   Ibid., 

PL  XL  c,  figs.  14,  15. 
Reference    to     Chimxra    (Ischyodon)    centertrii. 

Ibid.,  p.  345. 
Reference  to  Chimaera   (Psittacodon)   sedgwickii. 

Ibid.,  p.  349,  PI.  XL,  figs.  17,  18. 
Reference    to    Chimasra    (Psittacodon)    mantelli. 
Ibid.,  p.  348,  PL  XL  a,  figs,  i,  2,  Vol.  Ill,  1843. 
Reference  to  Chimaera(Ischyodon)agassizii.   Ibid., 
p.  341,  PL  XL  a,  figs.  3,  4  ( ?s),  PL  XL  c,  figs.  16 
(non  figs.  14,  15). 
Reference  to  Edaphodon  bucklandi.     Ibid.,  p.  351, 

PL  XL  d,  figs.  1-4,  9-12,  19-24. 
Reference  to  Edaphodon  eurygnathus.  Ibid.,  p.  352. 
Reference  to  Edaphodon  leptognathus.     Ibid.,  p. 

352,  PL  XL  a,  figs.  5-8,  13-18. 
Reference  to  Ischyodus  [=Chimaera  (Ischyodon)] 

helvetica.    Ibid.,  p.  345,  PI.  XL  c,  figs.  20,  21. 
AMMON,  LUDWIG  VON. 

1896.  Ueber     neue     Stiicke     von     Ischyodus.     Berichte 
Naturwiss.    Ver.    Regensburg,    Heft    5    (Fest- 
schrift), 1894-95,  pp.  253-263,  2  Taf.,  i  fig.   (I. 
schtipleri,  avitus). 
1899.  Ein    schemes    Exemplar    von    Ischyodus    avitus. 

Geogn.  Jahresh.,  Vol.  XI,  pp.  158-160,  I  Taf. 
BASSANI,  F. 

1901.  Reference  to  Chimaera  bucklandi  in  "Sue  alcuni 
avanzi  di  pesci  del  pliocene  toscano."     Monitore 
Zoologico  Italiano,  Vol.  XII,  N.  7,  p.  189. 
BENSTED,  W.  H. 
1862.  Reference  to  Ischyodus  agassizii.     Geologist,  Vol. 

V,  p.  378  (errore). 
BESSELS,  E. 

1869.  Reference  to  egg-case  of  Plschyodus  (Jurassic  of 
Wiirttemberg).     Jahreshefte   d.   Ver.   f.   vaterl. 
Naturkunde  in  Wiirtt.,  Vol.  XXV,  p.  152,  PL  in. 
BUCKLAND,  W. 

1835.  Chimaera  egertonii,  townsendii,  and  mantellii ;  also 
Chimxra  agassizii.  Proc.  Geol.  Soc.  Lond.,  Vol. 
II,  p.  206;  v.  also  in  Phil.  Mag.  (3),  Vol.  VIII, 
p.  5,  1836. 

1838.  Reference  to  Passalodon  (Syn.  Edaphodon). 
Proc.  Geol.  Soc.  Lond.,  Vol.  II,  p.  687. 

COOMARASWAMY,  A.   K. 

1903.  List  of  Fish  Teeth  of  Bagshot  Lands  (London 
Basin),  etc.  Proc.  Geol.  Assoc.  Lond.,  Vol.  IX, 
pp.  83-84. 


1 68 


LITERATURE   LIST. 


COPE,  E.  D. 

1869.  Reference  to  Edaphodon    (=Ischyodus)    monolo- 
phus.     Proc.  Bost.  Soc.  Nat.  Hist.,  p.  314. 

Reference  to  Edaphodon  (=Ischyodus)  smocki. 
Ibid.,  p.  316. 

Reference  to  Ischyodus  (mirificus,  smocki,  mono- 
lophus,  divaricatus).  Ibid.,  p.  314. 

Reference  to  Sphagepcea  aciculata.  Proc.  Amer. 
Philos.  Soc.,  Vol.  XI,  p.  241. 

Reference  to  Edaphodon  (Ischyodus)  divari- 
catus. Proc.  Bost.  Soc.  Nat.  Hist.,  p.  315,  and 
Vert.  Cret.  Form.  West.,  Vol.  II,  pp.  185-292, 

1875. 

Reference  to  Leptomylus  densus.  Proc.  Bost. 
Soc.  Nat.  Hist,  Vol.  XII,  p.  313. 

1871.  Reference    to    Leptomylus    cooki.      Proc.    Amer. 

Philos.  Soc.,  Vol.  XI,  p.  384. 
Reference     to     Edaphodon     (Ischyodus)     lateri- 

gerus.     Ibid.,  p.  243. 
1875.  Reference     to     Edaphodon      (Ischyodus)    steno- 

bryus.     Vert.    Cret.    Form.    West.,    Rep.   U.    S. 

Geol.  Surv.  Territ.,  Vol.  II,  pp.  284-285. 
Reference   to   Edaphodon    (=Ischyodus)    triparti- 

tus.     Ibid.,  pp.  284,  286. 
Reference  to  Diphrissa.    Ibid.,  p.  283. 
Reference    to    Edaphodon    (Ischyodus)    eoccenus. 

Ibid.,  pp.  285-288. 
Reference    to    Edaphodon    (Ischyodus)    fecundus. 

Ibid.,  pp.  285,  290. 
Reference     to     Edaphodon    (Ischyodus)    gaskilli. 

Ibid.,  pp.  285,  290. 

Reference  to  Leptomylus  forfex.     Ibid.,  p.  281. 
Reference    to    Edaphodon    (Ischyodus)    incrassa- 

tus.     Ibid.,  pp.  285,  289. 
Reference  to  Edaphodon   (Ischyodus)  laterigerus. 

Ibid.,  pp.  284,  288. 
Reference    to    Edaphodon    (Ischyodus)    longiros- 

tris.     Ibid.,  pp.  284-287. 

Reference  to  Ischyodus  miersii.    Ibid.,  pp.  285,  292. 
Reference  to  Ischyodus  mirificus.     Ibid.,  pp.  285, 

291. 
1878.  Reference  to  Chimaeroids  in  classification  as  lower 

in  the  scale  than  sharks.     Proc.  Amer.  Assoc. 

Adv.  Sci.,  Vol.  XXVI,  p.  292. 
1884.  Reference  to  holocephali  as  giving  rise  to  selachii, 

ichthyotomi    (from    which    hyopomata    are    de- 
rived), dipnoi.    Amer.  Naturalist,  p.  255. 
1891.  General  notes  on  Chimasroids  in  Syllabus  of  Lec- 
tures on  Geology  and  Palaeontology.     Ginn  and 

Co.,  pp.  135. 
DAVIES,  W. 

1872.  On  the  rostral  prolongations  of  Squaloraja  poly- 

spondyla.     Geol.   Mag.,  Vol.  IX,  p.   145,   PI.  iv. 
DAVIS,  J.  W. ' 
1880.  Reference  to  similarity  of  species  of  Pleuracan- 

thus    and    Ischyodus,    and   general    resemblance 

of   base   of   spines   of   Ischyodus   and    Siluroid. 

Ann.  and  Mag.  Nat.  Hist.,  May,  p.  355. 
1883.  Detailed   reference   to   Jurassic   Petalodonts,   etc., 

in  Trans.  Roy.  Dub.  Soc.,  pp.  327-350. 


DAVIS,  J.  W. — (Continued.) 

1888.  Reference  to  Callorhynchus  hectori.     Trans.  Roy. 
Dub.  Soc.  (2),  Vol.  IV,  p.  41,  PI.  vn,  figs.  14-15'. 
Reference  to  Ischyodus  brevirostris.     Ibid.,  p.  42, 
PI.  vii,  figs.  10-13. 

1890.  Reference  to  Ischyodus  brevirostris.  Ibid.,  pp. 
414-415.  (Cretaceous  of  Scandinavia.) 

DEAN,  BASHFORD. 

1904.  Reference  to  position  of  Menaspis  armata.  Sci- 
ence, Vol.  XIX,  p.  253,  and  Am.  Geologist,  Vol. 
XXIV,  pp.  49-53,  PL  ii. 

DIXON,  F. 

1850.  Reference  to   Edaphodon   sedgwicki.     Foss.   Sus- 
sex, p.  203. 
Reference  to  Edaphodon  mantelli.     Ibid.,  p.  203, 

PI.   xxxiv. 
Reference   to   Edaphodon   eurygnathus.     Ibid.,   p. 

in,  PI.  x,  figs.  18,  19,  22;  PI.  xii,  fig.  5. 
Reference   to   Edaphodon   leptognathus.     Ibid.,   p. 
in,  PI.  x,  figs.  20,  21. 

EASTMAN,  C.  R. 

1898.  On  the  dentition  of  Devonian  Ptyctodontidae. 
Amer.  Nat.,  Vol.  XXXII,  pp.  473-488,  546- 
560,  50  figs.  Reference  to  Ptyctodus  obliquus, 
major,  molaris,  calceolus,  ferox,  compressus, 
panderi ;  Rynchodus  secans,  occidentalis,  exca- 
vatus,  rostratus,  major;  Palseomylus  predator, 
frangens,  crassus,  greenei ;  Ichthyodorulites. 

1898.  Reference  to  Ptyctodus  and  to  Synthetodus  (re- 
garded by  Eastman  as  dipnoan)  ( PChimaeroid) 
in  Ann.  Rep.  Iowa  Geol.  Surv.,  Vol.  VII,  pp. 
108-116,  PI.  i. 

1900.  Reference  to  Rhynchodus  major  in  Am.  Geol., 
Vol.  XXV,  pp.  391-392. 

1900.  Einige  neue  Notizen  iiber  devonische  Fischreste 
aus  der  Eifel.  Centralb.  Min.  Geol.  Pal.,  pp. 
177-178.  (Rhynchodus  emigratus.) 

1903.  A    peculiar   modification    amongst    Permian    Dip- 

noans.     Am.   Nat.,  Vol.   XXXVII,  pp.  493-495, 
2  figs.     ( ?Chimseroid  affinities.) 

1904.  On  the  dentition  of  Rhynchodus  and  other  fossil 

fishes.     Am.  Nat.,  Vol.  XXXVIII,  pp.  295-299, 

2  figs.     Rhynchodus  major,  rostratus,  pcrtenuis, 

emigratus   (=Ramphodus  tetrodon)  ;   Ptyctodus 

calceolus. 
EGERTON,  Sir  P. 
1843.  Reference  to  Ischyodus  colei.  Proc.  Geol.  Soc. 

Lond.,  Vol.  IV,  p.  156. 
Reference    to    Chimaera    (Ischyodus)    beaumonti. 

Ibid.,  pp.  155,  156. 
Reference    to    Chimaera    (Ischyodus)   emarginata. 

Ibid.,  pp.  154,  156. 

Reference  to  Chimaera  dufrenoyi.     Ibid.,  p.  155. 
Reference  to  Ischyodus  duvernoyi.     Ibid.,  p.  156. 
Reference  to  Elasmodus.    Ibid.,  p.  156. 
Reference  to  Ischyodus  townsendii.     Ibid.,  p.  156. 
Reference  to  Ischyodus  brevirostris.     Ibid.,  p.  156 

(name  only). 
Reference   to   Ischyodus   dutertrei.     Ibid.,   p.    156 

(dutertrii)  ;  Ischyodus  agassizi,  p.  156. 


LITERATURE  LIST. 


169 


EGERTON,  Sir  P. — (Continued.) 

Reference  to  Chimaera  dutertrei.     Am.  Mag.  Nat. 

Hist.,  Vol.  XII,  p.  469,  and  Proc.  Geol.  Soc., 

Vol.  IV,  p.  154. 
Reference  to  Ischyodus  sedgwicki.     Ibid.,  p.   156. 

1847.  Reference    to    Elasmodus    hunteri.     Proc.    Geol. 

Soc.  Lond.,  Vol.  Ill,  p.  351,  and  Ganodus  den- 

tatus,  p.  353. 
Reference  to  Ganodus  colei.     Quart.  Journ.  Geol. 

Soc.,  Vol.  Ill,  p.  352. 
Reference   to   Ischyodus.     Ibid.,   p.   351,   PI.   xm, 

fig.  i. 
Reference  to  Edaphodon  sedgwicki  and  Edapho- 

don  mantellii.     Ibid.,  p.  352. 
Reference  to  Edaphodon.     Ibid.,  p.  351,   PI.   xm, 

figs.  2,  3. 
1852.  Reference  to  Elasmodus  hunteri.     British  Fossils, 

Dec.,  Vol.  VI,  No.  i,  PI.  I. 

1869.  List  of  type  fossils  in  Egerton  Collection.  Refer- 
ence to  "Chiniaera."  Geol.  Mag.,  Vol.  VI,  p.  4. 

1871.  Ischyodus  orthorhinus.     Quart.  Journ.  Geol.  Soc., 

Vol.  XXVII,  p.  275,  PI.  xm. 

1872.  Reference     to     Prognathodus     (=Myriacanthus) 

giintheri.     Quart.  Journ.  Geol.  Soc.,Vol.  XXVIII, 
pp.  233-236,  PI.  vm. 

ElCHWALD,    E.    VON. 

1846.  Reference  to  Aulacosteus  (=Ptyctodus)  in 
Geognosy  of  Russia  (in  Russian).  According 
to  Leth.  Rossica,  Vol.  I,  pp.  15-48,  1860. 

EWALD. 

1848.  Describes    Menaspis    in    Monatsber.     Ber.    Akad. 

Wiss.,  p.  33.     Cf.  Neues  JB.  fur  Mineral.,  1849, 
p.   1 20. 

FiJRBRINGER,    K. 

1903.  Reference  to  Janassa  (lip  cartilages).  Morph. 
JB.,  Vol.  XXXI,  H.  2  u.  3,  pp.  364,  382. 

GEINITZ,  H.  B. 

1875.  Reference  to  Chimaera  mantelli.    Palseontogr.,  Vol. 

XX,  PI.  n,  p.  206,  PI.  xxxix,  figs.  11,  12. 
Reference  to  Chimaera  agassizii.     Ibid.,  p.  206,  PI. 
xxxix,  figs.  8-10. 

GERVAIS,  P. 

1869.  Reference  to  Dipristis  (  =  ?  Chimxra).  Zool.  et 
Pal.  Gen.,  p.  240. 

GIEBEL,  C. 

1856.  Reference   to   Menapis.     Zeitschr.   f.   d.   gesamm- 

ten  Naturwiss.  Berlin,  Bd.  VII,  p.  367,  Taf.  in 

and  iv. 

GILL,  THEO. 

1905.  Reference    to    a    Rhinochimaera-like    egg-capsule 

from     the     Laramie     (Cretaceous)     sandstone. 

Science,  N.  S.,  Vol.  XXII,  pp.  601-602. 

HAMY,  E.  T. 

1866.  Reference    to    Ischyodus    beaumontii.      Bull.    Soc. 

Geol.  France   (2),  Vol.  XXIII,  p.  656,  fig.  I. 
Reference   to   Ischyodus   sauvagei.     Ibid.,   p.   655, 

fig.  2. 


HASSE,  C. 

1885.  Reference  to  Squaloraja  polyspondyla.  Palaeon- 
togr.,  Vol.  XXXI,  p.  4,  PI.  i,  figs.  2,  3. 

HOWES,  G.  B. 

1890.  Reference    to    Squaloraja    (Chimaeroid)    exterm. 

Proc.  Zool.  Soc.  Lond.,  Dec.  2,  p.  687. 

1891.  Reference   to    Chimaeroid-like   column    of   Palaso- 

spondylus.  Trans.  Biol.  Soc.  Liverp.,  Vol.  VI, 
PJ44- 

HUENE,    F.    VON. 

1900.  Devonische  Fischreste  aus  der  Eifel.    Nat.  JB.  f. 

Min.,  Geol.  u.  Palaeontol.,  Vol.  I,  pp.  64-66. 
Reference    to    Rhynchodus    emigratus    v.    Huene. 
Centralb.   f.   Mineralogie,   I   p. 

JAEKEL,  O. 

1890.  Ueber  fossile  Ichthyodorulithen.     SB.  Gesell.  na- 

turforsch.  Freunde,  Berl.,  No.  7,  pp.  117-131. 
Oracanthus  bochumensis,  n.  sp.  Refers  this  to 
his  (order)  Trachyacanthidae. 

1891.  Ueber  Menaspis,  nebst  allgemeinen  Bemerkungen 

u.  d.  Systematische  Stellung  d.  Elasmobranchier. 
SB.  Gesell.  naturforsch.  Freunde,  Berl.,  No.  7, 
pp.  115-131,  PL  I- 

1892.  Reference  to  Chalcodus   permianus  as   equivalent 

to  Menaspis  armata :  not  a  Chimreroid,  as  Wood- 
ward believed,  but  a  "Trachyacanthid."  SB. 
Gesell.  naturforsch.  Freunde,  Berl.,  No.  9,  Nov. 
IS,  PP.  IS7-I58. 

Reference  to  Chalcodus  (=Menaspis)  and  to 
Reis's  referring  it  possibly  to  Chimaeroid.  SB. 
Gesell.  naturforsch.  Freunde,  Berl.,  No.  9,  pp. 
156-158. 

Ueber  Dichelodus  Gieb.  und  einige  Ichthyodoru- 
lithen. Eine  Entgegnung  an  Herrn  A.  Smith 
Woodward.  Neue  JB.  fiir  Mineralog.,  Vol.  I, 
pp.  6. 

1896.  Chimaeriden-Eier  aus  dem  unteren  Dogger  von 
Heininge  in  Wiirttemberg.  Zeitschr.  deutsch. 
geol.  Ges.,  Bd.  XLVIII,  p.  691. 

1899.  Ueber  d.  Organization  d.  Petalodonten.  Zeitschr. 
d.  deutschen  geol.  Gesellsch.,  Vol.  LI.  Heft  2, 
pp.  257-298,  PI.  ii. 

1901.  Ueber   jurassische   Zahne    und    Eier   von    Chima- 

riden.     Neues  JB.   Min.   Geol.   Pal.   Berl.,   Vol. 
XIV,  pp.  540-564,  PI-  4,  3  figs. 
Reference     to     Ischyodus     aalensis,     ferrugineus 
(=Aletodus  ferrugineus),  Callorhynchus  antarc- 
ticus. 

LEIDY,  J. 

1873.  Reference   to   Eumylodus.     Extinct   Vert.   Fauna 

W.  Territ.     (Rep.  U.   S.   Geol.   Surv.  Territ.), 

Vol.  I,  p.  309,  PI.  xix,  figs.  21,  22;  PI.  xxxvii, 

figs.  13,  14. 
Reference  to  Edaphodon  mirificus.     Ibid,  p.  306, 

and  Proc.  Acad.  Nat.  Sci.  Phila.  (1856),  p.  221. 


iyo 


LITERATURE  LIST. 


LERICHE,  M. 

1901.  Reference  to  Ischyodus  thurmani  and  to  Edapho- 

don   sedgwicki — of  the  latter  figuring  mandible 

and   a    (?)    spine.     Ann.   Soc.   Geol.   du   Nord, 

Vol.  XXXI,  p.  125-129.     Cf.  also  1903,  ibid.,  pp. 

239-252.     (Chimaeroids  in  Landenien.) 
1903.  Further   reference   to   these   genera.     Ibid.,   Vol. 

XXXII,  pp.  239-252. 
MANTELL,  G.  A. 
1844.  Reference   to   Chimsera.     Medals  of   Creation,   p. 

621. 

MARSH,  O.  C. 
1869.  Reference  to  Dipristis.     Proc.  Amer.  Assoc.  Adv. 

Sci.,  p.  230. 
Reference  to  Edaphodon  miersi;  Dipristis  miersii. 

Ibid.,  p.  230. 
MEYER,  H.  VON. 
1855.  Reference  to  Rhynchodus,  sp.  ind. :   ( Physichthys 

hoeninghausii.)    Palaeontogr.,   Vol.    IV,    PI.   xv, 

fig.  9  (errore). 

1859.  Reference     to     Ischyodus     acutus.     Palaeontogr., 

Vol.  VII,  p.  17,  PI.  II,  figs.  9-12. 
Reference     to     Ischyodus     (Chimaera)     rostratus. 
Ibid.,  p.  14,  PI.  ii,  figs.  3-8. 

1860,  Chimsera   (Ganodus)   prisca.     Neues  JB.,  p.  212. 

(Name  subsequently  withdrawn.) 

1862.  Chimaera  (Ganodus)  avita.     Palaeontogr.,  Vol.  X, 
p.  87,  PI.  xn. 

MONSTER,   G.  VON. 

1840.  Reference    to    Myriacanthus    franconicus.     Beitr. 

Petrefakt.,  Vol.  Ill,  p.  127,  PI.  in,  fig.  8. 
1842.  Myriacanthus  vesiculosus.     Ibid.,  p.   in,   PI.  vi, 

fig-  3- 

NEWBERRY,  J.  S. 
1871.  Reference  to  Rhynchodus. 
1873.    Palaeomylus     frangens :     Rhynchodus     frangens. 

Rep.  Geol.  Surv.  Ohio,  Vol.  I,  Ft.  II,  p.  311,  PI. 

xxvin,  figs.  2,  3. 

Reference  to  Rhynchodus.     Ibid.,  p.  307. 
Reference  to  Rhynchodus  secans.     Ibid.,  p.  310, 

PI.  xxvui,  figs.  1-3. 
Reference  to  Palaeomylus  crassus  (=Rhynchodus 

crassus).    Ibid.,  p.  312,  PI.  xxix,  fig.  3. 
1875.  Reference    to    Ptyctodus    calceolus.     Rep.    Geol. 

Surv.  Ohio,  Vol.  II,  Pt.  II,  p.  59,  PI.  LIX,  fig.  13. 

1877.  Reference  to  Rhynchodus  excavatus.     Rep.  Geol. 

Surv.  Wise.,  Vol.  II,  p.  397. 

1878.  Reference  to  Rhynchodus  occidentalis  and  exca- 

vatus.   Am.  N.  Y.  Acad.  Sci.,  Vol.  I,  p.  192. 
1889.  Reference    to    Palaeomylus    greenei    (Rhynchodus 

greenei).    Rep.  Geol.  Surv.  Ohio,  Vol.  I,  Pt.  II, 

P.  Si- 
Reference  to  Rhynchodus.    Mon.  XVI,  U.  S.  Geol. 

Surv.,  pp.  29,  45-51. 
Reference  to  Rhynchodus  crassus.    Ibid.,  pp.  49,  50, 

286,  ?H9,  PI.  xxvin,  fig.  4. 
Reference  to  Rhynchodus  excavatus.    Ibid.,  pp.  50, 

51,  288,  PI.  xxix,  fig.  i. 


NEWBERRY,  J.  S. — (Continued.) 

1889.  Reference  to  Rhynchodus  frangens.     Ibid.,  pp.  29, 

46,  48,  49,  288,  PI.  xxix,  figs.  2,  3. 

Reference  to  Rhynchodus  greenei.  Ibid.,  pp.  51,  62. 
Reference  to  Rhynchodus  occidentalis.  Ibid.,  p.  62. 
Reference  to  Rhynchodus  secans.  Ibid.,  pp.  29-46, 

47,  48,  286. 

Reference  to  Ptyctodus.    Ibid.,  pp.  62,  63,  68,  69. 
Reference  to  Ptyctodus  calceolus.    Ibid.,  p.  62. 
Reference  to  Chimaera.     Ibid.,  p.  46.     Townsendii 

of  Buckland,  perhaps  generically  identical  with 

Rhynchodus  frangens. 
NEWBERRY  and  WORTHEN. 

1866.  Reference  to  Rhinodus    (=Ptyctodus).     Palaeon- 
tology of  Illinois,  Vol.  II,  p.  106,  PI.  x,  fig.  10. 
NEWTON,  E.  T. 

1876.  On  two  Chimaeroid  Jaws  from  the  Lower  Green- 
sand  of  New  Zealand.    Q.  Jour.  Geol.  Soc.,  Vol. 

XXXII,  pp.  326-331,  PI.  xxi. 
Reference  to  Callorhynchus  hectori.    Quart.  Jour. 

Geol.  Soc.,  Vol.  XXXII,  p.  329,  PL  xxi,  figs.  6-9. 
Reference  to  Ischyodus  brevirostris.    Ibid.,  p.  326, 

PI.  xxi,  fig.  5. 
1878.  Chimaeroid  Fishes,  Brit.  Cret.  Rocks.    Mem.  Geol. 

Surv.,  Monogr.  IV,  p.  41,  PI.  xn,  figs.  1 1,  12. 

Reference  to  Callorhynchus  hectori. 
Reference  to  Elasmodectes.     Ibid.,  p.  43. 
Reference  to  Ischyodus  planus.     Ibid.,  p.  37,   PI. 

XII,  figs.  I,  2. 
Reference  to  Ischyodus  brevirostris.     Ibid.,  p.  27, 

PI.  ix. 

Reference  to  Ischyodus  latus.     Ibid.,  p.  32. 
Reference  to  Ischyodus  incisus.     Ibid.,  p.  38,  PI. 

xii,  figs.  3-10. 
Reference  to  Edaphodon  sedgwickii.     Ibid.,  p.  7, 

Pis.  i,  ii. 
Reference  to  Edaphodon  mantellii.     Ibid.,  PI.  iv, 

figs.  1-9. 
Reference   to   Edaphodon   agassizii.     Ibid.,   p.    12, 

PI.  ill. 
Reference   to    Edaphodon   crassus.    Ibid.,   p.   21, 

PI.  vn. 

Reference  to  Edaphodon  reedii.  Ibid.,  p.  19,  PI.  vi. 
Reference  to  Edaphodon  laminosus.  Ibid.,  p.  24, 

PI.  vni. 
Reference  to  Edaphodon  mirificus.     Ibid.,  p.  24. 

1881.  Reference  to  Ischyodus  townsendii.     Proc.  Geol. 

Assoc.,  p.  116,  fig. 
NIKITIN,  S. 

1882.  Reference  to  Edaphodon,  from  Cretaceous  of  Cen- 

tral Russia.    Mem.  Comite  Geol.,  Vol.  V,  No.  2, 

p.  42,  PI.  iv,  fig.  16. 
NOETLING,  F. 
1885.  Reference   to   Edaphodon   bucklandi.     AH.    geol. 

Specialk.    Preussen    u.  Thiiring.    Staaten,    Vol. 

VI,  Pt.  Ill,  p.  3,  PI.  i,  fig.  i. 
OWEN,  R. 
1840.  Reference  to  Elasmodus  hunteri,  extinct  Chimaera. 

Odontography,  Vol.  I,  p.  66. 


LITERATURE   LIST. 


171 


PANDER. 

1858.  Ueber  die  Ctenodipterinen  des  devonischen  Sys- 
tems St.  Petersburg.  Ref.  p.  50  to  structure  of 
dental  plates  of  Ptyctodus  as  combining  Gym- 
nodont  and  Chimaeroid  characters. 

PARENT,  H. 

1903.  Reference  to  Chimaeroids  in  Wealdon  of  Bas- 
Boulonnais,  in  Ann.  Soc.  Geol.  Nord,  Vol. 
XXXII,  pp.  17-48. 

PHILIPPI,  E. 

1897.  Ueber  Ischyodus  suevicus  nov.  spec.  Palaeontogr., 
Vol.  XLIV,  pp.  i-io,  PI.  n. 

PHILLIPS,  J. 

1871.  Reference  to  Ischyodus  egertoni.  Geol.  Oxford, 
p.  306,  PI.  xii,  fig.  24. 

PICTET,  F.  J. 

1854.  Reference  to  Edaphodon.  Palaeontologie,  ed.  2, 
Vol.  II,  p.  233. 

PICTET  and  CAMPICHE. 

1858.  Reference  to  Ischyodon  thurmanni.  Foss.  Terr. 
Cretace  St.-Croix  (Pal.  Suisse),  p.  76,  PI.  ix, 
fig.  8. 

PRIEM,  F. 

1901.  Reference  to  Edaphodon  bucklandi.  Bull.  Soc. 
Geol.  France,  49  sen,  Vol.  I,  p.  485. 

PROBST,  J. 

1882.  Reference  to  (fig.)  Chimaera  deleta  in  Jahreshefte 

d.  Ver.  f.  vaterl.  Naturw.  in  Wurtt,  pp.  120-131. 

QUENSTED,    F.    A. 

1852.  Reference  to  Chimaera  aalensis.  Handb.  Petrefakt, 
p.  185,  PI.  xiv,  figs.  14-16,  and  Der  Jura  (1858), 
PP.  339,  347,  PI-  XLVII,  figs.  21-28. 
Reference  to  Ischyodus  personal! :  Chimaera  per- 
sonati.  Ibid.,  ed.  I,  p.  185,  PI.  xiv,  fig.  17,  and 
Der  Jura,  p.  339,  PI.  XLVI,  figs.  8,  9. 

1858.  Reference     to     Chimaeracanthus     (=Ischyodus). 

Der  Jura,  p.  347. 

Reference  to   Chimaera   schuebleri.     Ibid.,  p.   782, 
PI.  xcvi,  fig.  39. 

1883.  Reference  to  Ischyodus  bifurcati :  Chimaera  bifur- 

cati.    Handb.  d.  Palreont.,  ed.  3,  p.  293,  PI.  xxm, 

fig.  25. 
REIS,  O.  M. 
1890.  Zur  Kenntnis     des     Skelets     der     Acanthodinen. 

Geognost.  JB.,  p.  30. 

1894.  Ueber  Phosphoritisirung  d.   Cutis,  d.  Testikel  u. 

d.    Riickenmarks.      (Reference    to    Ischyodus.) 
Arch.  mikr.  Anat.,  Vol.  XLIV,  pp.  87-119,  PI.  vi. 
?1892.  Ueber    d.     Kopfstacheln     b.     Menaspis     armata 
Ewald.     Mtinchen,  M.  Kutzner,  pp.  13. 

1895.  On  the  structure  of  the  frontal  spine  and  the  ros- 

tral-labial cartilages  of  Squaloraja  and  Chimasra. 

Geol.    Mag.    Lend.,    Decade    IV,    Vol.    II,    pp. 

38S-39I,  PI-  xn. 
RENAULT,  B.,  and  ZEILLER,  R. 
1886.  Reference   to    Fayolia   and    Palaooxyris    (Spiran- 

gium)   in  C.  R.  Acad.  Sci.  Paris,  Vol.  CVII,  p. 

1022. 


RlESS,   J. 

1887.  Reference  to  Ischyodus  schuebleri.     Palaeontogr., 

Vol.  XXXIV,  p.  17,  PI.  i.  fig.  8. 
Reference   to   Edaphodon   kilheimensis.     Ibid.,   p. 

20,  PI.  i,  fig.  ii. 

Reference  to  Chimaeropsis  paradoxa.    Palaeontogr., 
Vol.  XXXIV,  p.  21,  PI.  n,  figs.  9-11;  PI.  m,figs. 

I-IO. 

Reference   to   Ischyodon   quenstedti.     Ibid.,   p.   6, 

PI.  T,  figs.  l-S ;  PI.  n,  figs.  1-7. 
Reference  to  Ischyodus  avita.     Ibid.,  p.  14,  PI.  I, 

figs.  6,  7;  PI.  n,  fig.  8. 
Reference  to  Ischyodus  aalensis.    Ibid.,  p.  19,  PI.  i, 

fig.  9- 

Reference  to  Ischyodus  bifurcati :  Chimaera  bifur- 
cati.    Ibid.,  p.  19. 
Reference  to  Ischyodus  ferrugineus.     Ibid.,  p.  20, 

PI.  i,  fig.  10;  PI.  in,  fig.  ii. 
RILEY,  H. 
1833.  Reference    to    squaloraja    dolichognathos.     Proc. 

Geol.  Soc.  Lond.,  Vol.  I,  p.  484,  and  (2)  Vol.  V, 

p.  83,  PI.  iv. 
ROHON,  J.  V. 
1892.  Beitrag    zur    Kenntnis    der    Gattung    Ptycotodus. 

VH.  russ.  Kais.  mineralog.  Gesellsch.   St.   Pe- 
tersburg (2),  Vol.  XXXIII,  pp.  1-16,  PI.  i,  P. 

obliquus,  ancinnatus,  major. 
ROMANSKY,  H. 
1864.  Reference   to   spine   of   Myriacanthus   semigranu- 

latus.    Bull.  Soc.  Imp.  Nat.  Moscou,  p.  167,  Pt. 

II,  PI.  iv,  fig.  34. 
RUTOT,  A. 
1904.  Reference    to   fossil.     Chimaeroids    found    in   the 

neighborhood   of   Brussels  in   Bull.   Soc.   beige, 

Geol.  Pal.  Hydrol.,  Vol.  XVII,  pp.  383-499. 
SAUVAGE,  H.  E. 
1843.  Reference  to  Ischyodus  dutertrei.    Proc.  Geol.  Soc. 

Lond.,  Vol.  IV,  p.  89,  PI.  in,  figs.  17-19. 
1867.  Reference  to  Auluxacanthus  (^Ischyodus).  Catal. 

Poiss.    Form.    Second    Boulonnais    (Mem.    Soc. 

Acad.  Boulogne,  Vol.  II),  p.  63. 
Reference   to   Ischyodus   dufrenoyi.     Ibid.,   p.   73, 

PI.  iv,  fig.  12. 
Reference  to  Ischyodus  beaumontii.     Ibid.,  p.  83, 

PI.  iv,  figs.  4,  5. 
Reference  to  Ischyodus  rigauxi.    Ibid.,  p.  766,  PI. 

IV,  figs.  14,  15. 
Reference  to   Ischyodus  bouchardi.     Ibid.,   p.   81, 

PI.  iv,  fig.  6. 
Reference  to  Ischyodus  beaugrandi.    Ibid.,  Vol.  1 1, 

p.  79,  PI.  iv,  figs.  7,  8;  I.  sauvagei,  p.  86,  PI.  iv, 

figs.  2,  3. 
1896.  Les  Ischyodus  des  terrains  jurassiques  superieurs 

du   Boulonnais.     Bull.   Soc.   Geol.   France,    (3), 

Vol.  XXIV,  pp.  456-465,  PI.  ii. 
1902.  Les  Poissons  et  les  Reptiles  du  Jurassique  Supe- 

rieur  du  Boulonnais  au  Musee  du  Havre.    Bull. 

de    la    Soc.    Geol.    de    Normandie,    Vol.    XXI 

(1001),  pp.  3-4.     Reference  to  Ischyodus. 


172 


LITERATURE  LIST. 


SAUVAGE,  H.  E. — (Continued.) 

1903.  Noticia  sobre  las  peces  de  la  Caliza  litografica  de 
la  provincia  de  Leride  (Cataluna).  Memorias 
de  la  real  Academia  de  Ciencias  y  Artes  de  Bar- 
celona, Vol.  IV,  No.  35,  pp.  6-7.  Reference  to 
Spirangium  as  doubtfully  a  capsule  of  a  Chimas- 
roid.  PI.  i,  fig.  i. 

SEELEY,  H.  G. 

1864.  Reference  to  Edaphodon  huxleyi.  Ann.  and  Mag. 
Nat.  Hist.  (3),  Vol.  XIV,  p.  276  (name  only). 

TRAQUAIR,  R.  H. 

1003.  Reference  to  Gemiindina  (L.  Devonian)  "as  pos- 
sibly being  a  Chimaeroid."  Trans.  Roy.  Soc. 
Edinburgh,  Vol.  XL,  Pt.  IV,  p.  736. 

WAGNER,  A. 

1857.  Reference    to    Chimaera    (Ischyodon)    quenstedti. 

Gelehr.  Anz.  k.  bay.  Akad.,  Vol.  XLIV,  p.  288. 
1862.  Reference    to    Chimaera    (Ischyodon)    quenstedti. 

Abh.  math.-phys.  Cl.  k.  bay.  Akad.  Wiss.,  Vol. 

IX,  p.  286,  PI.  i,  fig.  i. 

WALCOTT,  C.  D. 

1892.  Preliminary  notes  on  the  Discovery  of  Vertebrate 

Fauna  in   Silurian    (Ordovician)    Strata.     Bull. 

Geol.   Soc.  America,  Vol.  Ill,  pp.   153-172,  Pis. 

m-v.    Reference  to  "Chimaeroid"  on  pp.  163-166. 

WEYL,  T. 

1884.  Squaloraja    polyspondyla     (foss.).    Hasse.    Palae- 

ontogr.  (3),  Vol.  VII,  p.  4,  PI.  i,  figs.  2  and  3. 

Oligocene  of  Palmnicken. 
WOODWARD,  A.  S. 
1886.  Reference  to  Squaloraja  polyspondyla.    Proc.  Zool. 

Soc.  Lond.,  p.  527,  PI.  LV,  figs.  1-5,  7,  8,  and  1887, 

p.  481. 
Reference  to  Squaloraja  tenuispina.     Ibid.,  p.  530, 

PI.  LV,  fig.  6. 
Note    on    the    lateral    line    of    Squaloraja.     Ibid., 

p.  481. 
Anatomy   and    systematic   position   of   Squaloraja 

polyspondyla.     Ibid.,   pp.   527-528.     PI.   LV,   and 

1887,  p.  481. 
1888.  Reference    to    English     Cretaceous     Chimaeroids, 

Ischyodus,     Edaphodon,    and    Elasmodectes     in 

Proc.  Geologists'  Ass.,  Vol.  X,  No.  5,  pp.  209- 

301,  333- 

Reference  to  absence  of  Chimaeroids  in  the  Mount 
Lebanon  Cretaceous  in  Rep.  British  Ass.,  Sec.  C. 


WOODWARD,  A.  S. — (Continued.) 

1889.  On  the  Myriacanthidas,  an  extinct  family  of  Chi- 
maeroid fishes.  Ann.  N.  H.  (6),  Vol.  IV,  pp. 
275-280.  A  new  family  to  include  Myriacanthus, 
Ag.  and  Chimaeropsis,  Zittel. 

1889.  Reference     to     Myriacanthus     paradoxus.     Ann. 

Mag.  Nat.  Hist.  (6),  Vol.  IV,  p.  279. 
Reference     to     Ischyodus     egertoni.     Palaeont.    in 
Maiden    Mus.    Geol.    Mag.,    Dec.    Ill,    Vol.  VI, 
p.  363. 

1890.  Reference  to  Ganodus  oweni.     Proc.  Geol.  Ass'n, 

Vol  XI,  p.  303,  PI.  in,  fig.  4. 

1891.  Detailed   reference   to   fossil   Chimaeroids.     Cata- 

logue of  Fossil  Fishes  of  British  Museum,  Vol. 
II,  pp.  xvi,  37. 

Critique  of  Jacket's  Menaspis  and  Trachyacanthid 
papers.  Geol.  Mag.,  Sept. 

Reference  to  Elasmodus  greenoughi  (Belgian  Neo- 
zoic). Ibid.,  Dec.  Ill,  Vol.  VIII,  No.  321,  pp. 
112-113. 

1892.  Reference  to  supplementary  observations  on  some 

fossil  fishes  of  the  English  Lower  Oolites.   Proc. 

Geologists'  Ass'n,  Vol.  XII,  pp.  238,  239. 
On  the  skeleton  of  a  Chimaeroid  fish   (Ischyodus 

egertoni?)   from  the  Oxford  Clay  of  Christian 

Malford,  Wiltshire.     Ann.  Mag.  Nat.  Hist.  (6), 

Vol.  IX,  pp.  94-96. 
On  some  teeth  of  new  Chimaeroid  fishes  from  the 

Oxford     and     Kimmeridge     clays    of    England. 

Ann.  and  Mag.  Nat.  Hist.,  July,  pp.  13-16,  PI.  in. 

Reference  to   Pachymylus   leedsii,   Brachymylus 

altidens  and  minor,  Elasmodectes  secans. 
1898.  Review  of  fossil   Chimaeroids.     Vertebrate   Palae- 
ontology, pp.  54-61. 
WOODWARD  and  SHERBORN. 
1890.  Reference  to  fossil  Chimaeroids.     Cat.  Brit.  Foss. 

Vertebrata. 
ZITTEL,  K.  A.  VON. 
1887-90.  Reference  to  Chimaeropsis  paradoxa.  Handb. 

d.  Palaeont.,  Vol.  Ill,  p.  114,  fig.  126. 
Reference  to  Chalcodus  permianus.     Ibid.,  p.  72, 

fig.  66. 
Reference    to    Metopacanthus    (=Myriacanthus). 

Ibid.,  p.  no. 
Reference  to   Metopacanthus  orthorhinus.     Ibid., 

p.  in. 


EXPLANATION  OF  PLATES. 


PLATE  I. 
THE  DEPOSITING  OP  THE  EGG  OF  CHIMERA  COLUEI. 

(All  figures  about  natural  size. ) 

a.        Anus.  l.g.  Lime  gland. 

c.         Crease  in  tumid  eminence  in  median  ventral  line,  m.  Cord  representing  rudiment  of  dorsal  mesentery, 

just  posterior  to  opening  of  oviducts.  Fig.  2.                                   and    containing  the   posterior    mesenteric 

c.         Crease    in    oviduct    in   which    marginal  web    of                                   vessels. 

capsule  was  laid  down.     Fig.  4.  o.  Ovary. 

c.  a.     Tumid  eminences  formed  by   prolapsed  ends  of           op.  Opening  of  oviducal  sinus  into  cardinal  sinus. 

oviducts.  ovd.  Oviduct. 

c.  f.    Capsular  filament.  ovd.  a.  Oviducal  artery. 

c.o.     Capsular  organ  of  attachment.  ovd.  s.    Oviducal  sinus. 

c.  s.     Cardinal  sinus.     (Margin  of. )  p.  Urinary  papilla. 

/.         Funnel  of  oviduct.  r.  Folds  at  lower  end  of  rectum. 

h.         Heart.  r.s.  Receptaculum  seminis. 
/.          Liver. 

Fig.  i. — Preparation  of  gravid  female,  showing  eggs  in  oviduct.  The  egg-capsules  are  well  formed, 
the  egg-containing  portion  situated  in  the  hinder  portion  of  the  oviduct.  The  external 
openings  of  the  oviduct  protrude  from  the  body.  The  receptaculum  seminis  is  shown  at 
r.  s.  The  oviducts  extend  far  forward  ;  their  single  opening  appears  at  /.,  immediately 
behind  the  position  of  the  heart,  h.  The  mesovarium  is  greatly  restricted;  it  can,  how- 
ever, be  distinguished  on  the  left  side  of  the  figure  where  the  capsular  gland  has  been 
drawn  out.  The  oviducal  artery  is  extremely  conspicuous  at  this  stage. 

Fig.  2. — Region  of  ventral  fins  of  a  specimen  which  has  recently  deposited  eggs,  showing  the  pro- 
lapsed ends  of  the  oviducts. 

Fig.  3. — Filamentous  end  of  egg-capsule  showing  bulb-shaped  organ  of  attachment.  After  sketch 
by  Professor  Wilbur. 

Fig.   3  a. — Filamentous  end  of  similar  capsule. 

Fig.  4. — Preparation  showing  oviducts  of  a  specimen  about  to  deposit  egg-capsules.  The  oviducts, 
as  shown  in  fig.  i,  pass  back  on  either  side  from  the  median  funnel,  f.  The  one  at  the 
right  in  the  figure  is  shown  lying  in  a  capacious  blood-filled  sac  of  the  peritoneum,  ovd.  s. 
This  sinus  is  slung  from  the  dorsal  wall  of  the  body  cavity  :  its  sides  (right  and  left) 
draw  closer  together  as  they  leave  the  oviduct  and  approach  the  (dorsal)  wall  of  the 
body  cavity.  And  here  appears  finally  a  series  of  openings,  op.,  through  which  blood  of 
the  oviducal  sinus  obtains  free  communication  with  the  cardinal  sinus,  c.  s.  It  is  evident,  of 
course,  that  the  oviduct,  ovd.,  is  bathed  in  the  blood  contained  in  the  sinus;  and  that  it  can 
well  be  seen  only  where  it  lies  against  the  wall  of  the  sinus,  the  blood  then  forming  the  dark- 
red  masses  at  either  side  of  the  oviduct.  The  preparation  has  been  made  so  that  the 
external  opening  of  one  oviduct  is  retained.  From  it  one  sees  protruding  the  narrow 
end  of  the  egg-capsule.  The  opposite  oviduct  is  shown  opened.  The  details  of  the  lime 
gland  appear  at  /.  g.  Immediately  below  it  from  a  transverse  fold  in  the  oviduct  arises 
the  viscid  secretion,  c.  o.,  which  draws  together  posteriorly  and  becomes  the  capsular 
filament,  c.  f.  One  observes  many  creases  in  the  wall  of  the  oviduct.  In  the  deepest, 
c.,  the  lateral  web  of  the  egg-capsule  is  laid  down.  The  creases  are  especially  note- 
worthy near  the  hinder  opening  of  the  oviduct.  Here  its  muscular  walls  serve  to  hold  the 
capsule  as  it  hangs  in  the  water  while  the  remainder  of  the  capsular  filament  is  being  devel- 
oped. 


CHIMAERA 


PLAT 


f>vd,a- 


ilVil  II 


• 


Litl:  AnstvWerner&Wuner,  Frankfu 


PLATE  II. 
OVIDUCT  OF  CHIMERA  COLUEI  AND  MODE  OF  FORMATION  OF  THE  EGG-CAPSULE. 

(All  figures  natural  size,  excepting  the  last,  fig.  n.) 


b. 
c. 


c.p. 
d.  k 
l.w. 

Fig. 


Line  in  which  the  lip  of  the  operculum  separates  m- 

from  the  side  of  the  capsule. 
Blastoderm. 
Aperture  (cervix)  through  which  the  anterior  end  of  m.  o. 

the  capsule  is  beginning  to  protrude.  o. 

Capsular  gland.     In  this  region  a  series  of  trans-  oi'd. 

verse  zones  can  be  made  out  extending  as  far  ovd.  a. 

posteriorward  as  t.  o.  o^>d.  s. 

Foldings  in   the  margin  of  the  capsule  in  which  r. 

later  appear  the   perforations  in  the  caudal 

sheath.  *• 

Groove  in  which  dorsal  keel  of  egg-capsule  is  laid  /.  o. 

down.      At  either  side  of  this  are  thickened 

areas  which  form  the  dorsal  wall  of  capsule. 
Folds   in  oviduct,  in  which  the  lateral  web  of  the  t.  s. 

capsule  is  laid  down. 


Rudiment  of  mesentery  of  gut  containing  ves- 
sels. This  lies  behind  oviduct  (cf.  plate  I, 
figs,  i  and  4). 

Mesovarium. 

Ovum  about  to  break  from  the  ovary. 

Oviduct. 

Oviducal  artery. 

Oviducal  sinus. 

Folds  in  groove  of  lateral  web  by  which  the 
rugae  of  the  capsule  are  established. 

Stigma. 

Folds  under  the  edge  of  the  lime  gland  in  which 
the  terminal  organ  of  the  filamentous  capsule 
is  laid  down. 

Thickened  area  in  which  is  molded  one  side  of 
the  tail-sheath. 


Fig, 
Fig. 


Fig, 


Fig. 
Fig. 


Fig, 


5. — Ovary  and  oviduct  of  left  side,  showing  egg  about  to  be  taken  into  the  oviduct.  The  ovary 
is  closely  enveloped  in  the  mesovarium,  m.  o.,  the  fold  of  which  is  continued  back,  encloses 
the  oviduct  and  shows  at  ovd.  s.  the  beginnings  of  the  oviducal  sinus.  It  will  be  observed 
that  the  egg,  o.,  about  to  escape  from  the  ovary,  is  of  great  size.  This  is  due  to  its  fluid 
consistency  at  this  stage,  its  contents  having  spread  out  when  the  preparation  was  made. 
A  conspicuous  stigma  is  present,  to  which  nutrient  blood-vessels  converge.  At  this  stage 
the  oviduct  is  situated  close  to  the  dorsal  wall  of  the  cavity  of  abdomen.  In  later  stages, 
during  growth  of  the  capsule,  the  oviduct  hangs  down  freely  into  the  abdomen  and  is 
bathed  by  the  blood  in  the  enlarged  sinus,  ovd.  s. 

6. — Preparation  of  oviduct  from  which  a  developing  capsule  was  removed,  showing  the  fold- 
ings of  the  lining  membrane  which  serve  in  modeling  the  capsule. 

7. — Preparation  of  anterior  end  of  oviduct,  showing  a  portion  of  the  egg-capsule  in  situ.  This 
figure  illustrates  the  "segmental"  character  of  the  capsular  gland,  for  each  segment  of  which 
vessels  are  provided  by  the  oviducal  artery.  The  narrow  end  of  the  egg-capsule  is  shown 
within  the  oviduct ;  at  t.  p.  foldings  are  shown  in  its  marginal  walls,  which  later  produce 
the  perforations  of  the  caudal  sheath.  At  either  side  of  the  deep  groove,  d.  k.,  in  which 
the  dorsal  keel  of  the  capsule  is  molded,  appears  a  mass  of  glandular  tissue.  This  is  out- 
rolled  on  either  side  into  the  marginal  creases  in  which  the  lateral  web  of  the  capsule  is 
being  laid  down. 

8. — Immature  capsule  containing  egg.  The  tail  end  of  this  capsule  was  incomplete,  but  by 
means  of  a  ligature  it  was  so  preserved  that  the  egg  was  incubated.  By  the  tension  of  the 
ligature,  however,  the  shape  of  the  capsule  was  somewhat  altered  and  the  egg  became  more 
spherical  in  form.  The  lateral  web  of  this  capsule  is  delicate  and  extremely  wide. 

9. — Egg-capsule  opened,  showing  shape  into  which  the  egg  is  elongated  during  incubation. 
io, — Egg-capsule  at  about  the  time  of  deposition,  defective  only  in  its  terminal  filament.  This 
was,  in  fact,  deposited  while  the  fish  was  in  captivity.  From  this  figure  one  obtains  an 
idea  of  the  translucency  of  the  freshly  deposited  capsule. 

ii  and  Fig.  n  a-c. — Details  in  structure  of  egg-capsule.  Fig.  n  shows  a  detail  in  the  struc- 
ture of  the  opening  valve.  The  fold  in  the  wall  near  apex  of  capsule,  a.  /.,  passes 
upward  and  inward  into  a  ridge,  the  walls  of  which  are  folded  into  thickened  and  thinner 
areas  alternately.  At  a.  a  transverse  section  shows  height  of  this  ridge.  At  b.  appears  a 
lateral  view  of  the  same  ridge,  indicating  how  it  is  made  up  of  alternating  elements.  By 
a  process  of  weathering  in  the  thin  intervening  areas  fenestrae  are  formed  which  insure 
respiration  and  which  later,  by  a  continued  process  of  weathering,  break  open  the  valve  of 
the  capsule.  In  fig.  n  c.  is  shown  the  continuation  of  this  folding  process,  occurring  at 
sides  of  tail  region  of  capsule.  By  the  weathering  of  the  thin  spaces  between  the  folds  res- 
piratory openings  are  gradually  formed. 

176 


CHIMAERA 


PLATE  n. 


tn.o.  ovd.a. 


/ 


il 


ashford  Dean  del.  • 


Lith.Anstv  Werner  iWinter,  Frankfurt'-M 


oT  c." 

• ;  '. 
•  c 


PLATE  III. 
THE  EGG-CAPSULE  OF  CHIMERA  COLLIEI  SHOWN  AT  DIFFERENT  STAGES  OF  DEVELOPMENT. 

( All  figures  about  natural  size.) 

Fig.  12. — Capsule  at  the  stage  of  the  fertilization  of  the  egg.  The  lowermost,  i.  e.,  valve-bearing, 
end  of  the  capsule  is  fairly  complete,  but  its  substance  is  delicate.  The  present  capsule 
collapsed  during  the  process  of  removing  it  from  the  oviduct ;  the  egg  it  contained  rup- 
tured and  flowed  out  through  the  unfinished  end. 

Fig.  13. — Capsule  slightly  older  than  the  preceding.  The  opening  end  is  of  firmer  consistency ; 
the  lateral  web  is  well  formed  and  somewhat  pigmented. 

Fig.  14. — Capsule  slightly  older  than  the  preceding.  The  lateral  dorsal  webs  are  more  perfectly 
formed. 

Fig.  15. — Capsule  in  which  the  tail-sheath  is  beginning  to  be  formed. 

Fig.  16. — Egg-capsule  in  which  the  egg-inclosing  portion  is  nearly  completed.  The  tail-sheath  is 
still  a  shapeless  mass.  The  lateral  webs  are  widest  at  this  stage  ;  they  later  become 
molded  more  closely  and  their  delicate  margins  wear  away  soon  after  the  egg  is  deposited. 
Rugae  are  appearing  near  the  posterior  end  of  the  capsule.  An  egg  at  this  stage  can  be 
incubated  if  a  ligature  is  placed  near  the  base  of  the  caudal  sheath.  (In  figs.  12  to  16 
capsules  are  shown  in  dorsal  aspect.) 

Fig.  17. — Egg-capsule  from  which  embryo  has  been  naturally  hatched.  This  is  the  most  perfect  of 
the  specimens  which  the  writer  dredged  in  Puget  Sound.  Its  lateral  webs  are  still 
largely  uninjured,  the  filamentous  tip  alone  being  defective — lacking  the  bulbous  organ  of 
attachment.  The  ventral  aspect  is  here  shown,  and  we  note  at  d.  h.  the  enlargement  of  the 
wall  of  the  capsule  in  which  the  mandibular  region  of  the  young  fish  comes  to  lie.  The 
figure  shows  also  the  close  laminae  in  which  the  substance  of  the  capsule  is  laid  down. 

Fig.  17  a. — Capsule  of  foregoing  figure  shown  in  lateral  aspect.  The  valve  of  the  capsule  is  repre- 
sented as  opened,  a  position  assumed  naturally  only  at  the  time  of  the  escape  of  the  young 
fish,  the  valve  and  its  springy  mechanism  reminding  one  of  the  "mouth"  of  the  corolla  of  a 
labiate  plant.  This  figure  shows  the  ridges,  r.  and  /.,  which  overlap  (r.  overlapping  /.) 
up  to  time  the  young  fish  escapes.  It  shows  also  how  the  neighboring  tip  of  capsule 
weathers,  leaving  only  three  eminences  protruding,  of  which  the  one  belonging  to  the  lid  of 
the  valve  is  the  longest.  The  dorsal  keel  of  the  capsule  is  here  well  shown,  d-  k.  It 
varies  little  in  height  and  passes  nearly  the  whole  length  of  capsule. 

Fig.  17  b. — Capsule  of  foregoing  specimen  shown  in  dorsal  aspect.  This  specimen  shows  adequately 
the  extent  and  character  of  the  rugae  of  the  lateral  web.  At  its  anterior  end,  at  r. ,  appears 
the  rim  of  the  valvular  opening.  In  a  capsule  from  which  the  fish  has  naturally  escaped 
this  ridge  no  longer  returns  to  its  former  position  under  the  ridge  /. 

Fig.  17  c. — Capsule  of  foregoing  specimen  shown  from  in  front.  This  figure  was  prepared  to  illus- 
trate the  character  of  the  overfolded  margins  of  opercular  opening,  and  the  peculiar  curving 
of  the  sides  of  valve.  It  shows  also  the  prominence  of  the  dorsal  keel. 

(The  capsule  of  fig.  17  is  somewhat  light  colored  for  one  which  has  been  long  deposited.    Old  capsules  are  usually 
greenish  black  in  color.) 


CHIMAERA 


PLATE  in. 


13 


14 


17  » 


ka  del. 


LithAns'v.Wen'.erJ. Winter,  Frdnkfurla/M. 


PLATE  IV. 
STAGES  OF  FERTILIZATION,  SEGMENTATION,  AND  BLASTULA. 

(Preparations  magnified  about  15  diameters.     All  drawings  from  fresh  material.     Figs.  22  to  28  from  camera  drawings 
of  embryos  which  had  been  removed  from  the  egg  and  viewed  as  transparent  objects.) 

Fig.  1 8. — Late  stage  of  fertilization.    The  oblong  shape  of  the  germinal  area  is  due  to  artifact.    The 

preparation  illustrates  the  number  and  size  of  the  entrance  pits  of   spermatozoa  and  the 

extent  of  the  marginal  groove. 
Fig.  19. — Later  stage  of  fertilization.     This  indicates  the  extent  of  the   marginal  groove  and  the 

difference  in  size  of  the  entrance  pits  of  the  spermatozoa. 
Fig.  20. — Stage  showing  in  surface  view  a  single  furrow.     As  already  noted,  however,  this  stage  is 

not  one  of  first  segmentation,  since  it  contains  several  segmentation  nuclei.      Surrounding 

the  germinal  area  is  a  narrow  groove  margined  outwardly  by  eminences  containing  sperm 

nuclei. 

Fig.  21. — Stage  similar  to  foregoing,  but  showing  at  the  surface  four  ''  blastomeres." 
Fig.  22. — Stage  of  early  segmentation.     Here  the  marginal  areas  containing  sperm  nuclei  are  far 

less  conspicuous. 

Fig.  23. — Stage  similar  to  the  preceding. 
Fig.  24. — Stage  of  segmentation. 

Fig.  25. — Stage  of  late  segmentation.     Blastomeres  in  resting  stage. 
Fig.  26. — Stage  of  late  segmentation. 
Fig.  27. — Stage  of  late  segmentation.     The  darker  color  of   the  central  blastomeres  indicates  a 

greater  depth  in  this  region  of  the  germ. 
Fig.  28. — Blastula.     In  this  stage  inter-blastomeral  lines  were  traced  over  the  light-colored  circum- 

germinal  ring. 
Fig.  29. — Blastula.      Viewed  as  an  opaque  object,  and  showing  a  sharply  marked  boundary  between 

the  blastoderm  and  the  circumgerminal  ring. 


180 


18 


ft 


PLATE  V. 
BLASTULA,  GASTRUI,^,  AND  EARLY  EMBRYOS. 

(Preparations  magnified  about  15  diameters.     In  Figs.  30-34  the  circumgerminal  zone  has  been  inaccurately  litho- 
graphed ;  it  should  appear  less  conspicuous,  its  outer  margin  merging  insensibly  into  the  surrounding  yolk.) 

Fig.   30. — Late  blastula,  showing   especially  the  extent  of  the  circumgerminal  ring  and  its  irregular 

margin. 
Fig.  31. — Early  gastrula.     The  transverse  shadow  at  the  lower  end  of  the  germinal  area  represents 

the  beginnings  of  the  archenteric  cavity. 

Fig.   32. — Early  gastrula,   showing  the  extent  of  the  archenteric  space- 
Fig-   33- — Gastrula,  showing  the  appearance  of  the  head  region  of  the  embryo.     In  this  preparation 

merocytes  could  be  distinguished  in  the  outer  part  of  the  circumgerminal  ring. 
Fig.   34- — Gastrula,  showing  the  early  embryo  and  the  extent  of  the  segmentation  cavity. 
Fig-   35- — Gastrula,  slightly  older,    showing  the  early  vascularization  of  the  blastoderm. 
Fig.   36. — Gastrula,  showing  early  embryo  at  a  stage  corresponding  with  Balfour's  stage  c  in  the 

shark. 

Fig.   37. — Blastoderm,  showing  embryo  at  a  stage  corresponding  with  Balfour's  stage  F  in  the  shark. 
Fig.   38. — Blastoderm  and  embryo  at  a  stage  corresponding  with  Balfour's  stage  G  in  the  shark. 


182 


CHIMAERA 


30 


31 


A    B 


PLATE  v 


°^    A 


A    B 


33 


34 


37 


38 


PLATE   VI. 
DETAILS  OF  EARLY  EMBRYOS. 

a.  Archenteron.  »•  Neurenteric  opening. 

ec.  Ectoderm.  of.  Optic  vesicle. 

fill.  Entoderm.  /«•  Pronephric  region. 

ffi.  g-n.  First  and  second  gill-clefts.  v.  i.  Vitello-intestinal  vein. 

A.  Heart. 

Fig.  39. — Detail  of  embryo  shown  in  plate  i,  fig.  35,  viewed  as  an  opaque  object. 

Fig.  39  a-e. — Same  embryo  viewed  in  various  positions  as  transparent  object. 

Fig.  40. — Embryo  shown  in  plate  vi,  fig.  36,  viewed  as  a  transparent  object. 

Fig.  41. — Embryo  shown  in  plate  vi,  fig.  37,  viewed  as  a  transparent  object. 

Fig.  41  a. — Embryo  shown  in  plate  vi,  fig.  38,  viewed  as  an  opaque  object. 

Fig.  41  b. — Embryo  shown  in  plate  vi,  fig.  38,  viewed  as  a  transparent  object. 


184 


CHIMAERA 


PLATE  vi. 


39 


, 


40 


39  u 


41' 


( 

'         fl\ 


..  r 

..   B 


TiWinter,  Frjr 


PLATE  VII. 
LATBR  EMBRYOS. 

(Preparations  magnified  about  25  diameters.) 

a.  Anus.  ot.  Otic  vesicle. 

at.  Atrium.  ot.  o.  External  opening  of  otic  vesicle. 

b.  Epiphysis.  p.  Pineal  outgrowth. 

c.  Conus  arteriosus.  -p.  a.  g.  Postanal  gut. 
c.  e.  Caudal  eminence.  £n.  Pronephros. 

c.  v.  Caudal  vein.  fn,  d.  Pronephric  duct. 

gj,  g".  Gill  slits.  f.  f.  Pectoral  fin. 

k.  Cephalic  knob.  s.  Spiracle. 

of.  Optic  vesicle.  s.  v.  Sinus  venosus. 

v.  Ventricle. 

Fig.  42. — Embryo,  age  about  25  days,  corresponding  to  Balfour's  stage  G  (+)  of  shark.  This 
embryo  bent  during  the  process  of  fixation.  It  shows  especially  well  the  knob-like  out- 
growth, k.  in  the  region  of  the  forebrain. 

Fig.  42  a  and  b. — Anterior  region  of  preceding  embryo.  Shown  in  nearly  lateral  and  in  dorsal 
aspect. 

Fig.   43. — Embryo,  age  about  29  days,   corresponding  approximately  to   Balfour's  stage  i  in  shark. 

Fig.   43  b. — Anterior  region  of  specimen  similar  to  preceding. 

Fig.  44. — Embryo,  age  about  31  days,  corresponding  approximately  to  Balfour's  stage  j  in  shark. 
It  shows  a  bulbous  caudal  thickening. 

Fig.  45. — Embryo,  age  about  40  days,  corresponding  approximately  to  Balfour's  stage  K  in  shark. 
The  circular  area  under  the  letters  g.'  g."  was  found  to  be  artifact. 

Fig.  46. — Embryo,  age  about  45  days,  somewhat  more  advanced  than  Balfour's  stage  L  in  shark. 
At  the  time  of  fixation  the  embryo  probably  twisted,  so  that  its  axis  came  to  lie  nearly 
parallel  to  the  neighboring  margin  of  the  blastoderm.  (Length  of  embryo  20  mm.) 


186 


CHIMAERA 


PLATE  vn 


46 


iJthAnstyWerneri  Winter,  Fr.:.> 


.  •••      .  • 


PLATE  VIII. 
EMBRYOS  OF  CHIMERA  COLLIEI. 

ch.          Notochord.  sp.  Spiracle. 

n.  Neural  tube.  x.  Irregularity  in  line  of  postanal  gut.     Possibly  artifact. 

n.  c.       Neurenteric  canal.  y.  Yolk. 

/.  a.  g.  Postanal  gut.  y.  s.  Stalk  of  yolk-sac. 

Fig.  42  c. — Ventral  aspect  of  the  head  region  of  specimen  shown  on  plate  vn,  fig.  42.  This  indi- 
cates especially  the  extent  of  the  stomadeal  invagination. 

Fig.  46  a. — Detail  of  tip  of  tail  of  specimen  shown  in  plate  vn,  fig.  46.  It  illustrates  especially  the 
character  of  the  caudal  knob  and  the  extent  of  the  postanal  gut. 

Fig.  47. — Embryo  and  blastoderm  shown  attached  to  irregular  mass  of  yolk.  The  embryo  is  of  the 
stage  shown  in  plate  vn,  fig.  44.  It  will  be  seen  that  a  deep  crease  marks  the  line  of  sepa- 
ration of  blastoderm  and  yolk,  y. 

Fig.  47  a,  b. — Figures  showing  the  foregoing  specimen  in  natural  size.  These  give  an  idea  of  the 
extent  of  the  yolk  mass  around  which  the  blastoderm  is  growing. 

Fig.  47  c. — Margin  of  blastoderm  in  the  region  which,  in  fig.  47,  is  concealed  by  the  tail.  It  is 
here  slightly  nicked,  and  a  line  of  fusion  can  be  traced  in  the  direction  of  axis  of  embryo. 

Fig.  48. — Embryo  of  stage  shown  in  plate  vn,  fig.  45.  The  blastoderm  has  by  this  stage  almost 
entirely  inclosed  the  yolk  mass  noted  in  fig.  47.  A  small  portion  of  the  yolk  is,  however, 
seen  in  lower  part  of  figure.  The  figure  also  shows,  although  indistinctly,  a  line  of  fusion 
passing  from  the  embryo  in  the  direction  of  the  rim  of  the  blastoderm. 

Fig.  48  a. — Preceding  specimen  shown  in  posterior  aspect.  This  indicates  the  extent  to  which  the 
rim  of  the  blastoderm  has  inclosed  the  yolk.  The  irregularity  in  its  margin  is  due 
probably  to  artifact.  In  the  yolk  itself  masses  can  be  distinguished,  even  under  a  low 
power,  which  suggest  separate  blastomeres.  The  exposed  surface  of  the  yolk  is  somewhat 
irregular,  suggesting  that  a  portion  of  the  yolk  material  has  recently  become  detached.  The 
blastomeres  themselves  are  loosely  associated,  so  that  some  of  them  could  be  removed  with 
dissecting  needles.  Their  peripheries  are  not  quite  as  distinct  as  the  present  figure  indicates. 

Fig.  49. — Late  embryo.  Age  unknown  (probably  five  or  six  months),  corresponding  approximately 
to  Balfour's  stage  N  in  shark.  Although  this  specimen  was  examined  living,  and  was 
apparently  uninjured,  its  body  cavity  was  filled  with  blood  cells.  Observe  also  the 
enlarged  blood-knots  in  the  external  gills  and  the  position  of  the  spiracle  denoted  in  this 
figure  by  the  small  red  spot  immediately  above  the  rim  of  the  upper  jaw.  (Embryo's 
length  35  mm.) 

Fig.  49  a. — Dorsal  aspect  of  preceding  specimen.  This  pictures  more  clearly  the  blood-knots  of 
the  external  gills. 

Fig.  49  b. — Ventral  aspect  of  preceding  specimen.  This  shows  especially  the  masses  of  yolk,  y, 
attached  to  the  external  gills;  also  the  point  of  attachment  of  the  stalk  of  the  yolk  sac,  y.  s. 

Fig.  49  c. — Detail  of  facial  region  of  preceding  specimen,  indicating  the  extent  to  which  the  gill 
arches  protrude  at  the  side  of  the  head.  The  gill  filaments  are  cut  away,  but  from  their 
bases  one  observes  that  they  occur  only  on  the  anterior  rim  of  each  gill  slit. 

Fig.  49  d. — Lateral  aspect  of  preceding  specimen.  This  pictures  again  the  gill  region  from  which 
the  external  filaments  have  been  removed.  The  spiracle,  sp.,  is  seen  immediately  under 
the  eye. 


188 


CHIMAERA 


PLATE  vni. 


1-7'1 


1-7 ' 


D 


49b 


^ 


4-7' 


49C 


1-8' l 


T 


48 


nn  del. 


er,  Frankfurt^H 


PLATE  IX. 
LATE  EMBRYO  OF  CHIMERA  COLUEI. 

a.  cl.       Antero-pelvic  clasper.  mix.        Mixipterygium. 

a.  d.  p.  Anterior  dental  plate.  p.  d.  f.    Palatine  dental  plate. 

f.  o.         Frontal  organ. 

Fig.  50. — Late  embryo,  age  about  six  months,  corresponding  approximately  to  Balfour's  stage  P 

in  shark.     Lateral  view.     The  attachment  of  small  masses  of  yolk  to  the  side  of  the 

embryo  is  probably  artifact.     The  opercular  fold  has  here  been  partly  cut  away,  so  as  to 

expose  the  gills.      X  about  3. 

Fig.  50  a. — Ventral  aspect.     External  gills  removed  from  the  left  side. 
Fig.  50  b. — Dorsal  aspect. 
Fig.  50  c. — Anterior  aspect.      External  gills  removed  from  the  left  side.     Observe  particularly  the 

large  size  of  the  frontal  clasping  organ. 
Fig.  50  d. — Ventral   region,    showing  extent  to  which  the  opercular  fold  has   overgrown  the  gill 

lamellae.     A  detail  is  given  as  to  the  origin  of  the  external  filaments. 
Fig.  50  e. — Region  of  the  mouth.     This  shows  especially  the  appearance  of  the  sensory  canals  and 

the  early  condition  of  the  dental  eminences  and  of  the  labial  cartilages. 
Fig.  50  f. — Ventral  fin,  showing  the  early  condition  of  the  mixipterygium  and  of  the  antero-ventral 

clasping  organ. 
Fig-  5°  g- — External  gill  filaments,  giving  detail  of  vein  and  artery. 


190 


CHIMAL-RA 


PLATI-:  ix. 


Liih.Anst  v  Werner  iWimer.  Frankfurta/M. 


PLATE  X. 
"  OP  CHIMERA  COLLIEI. 

These    specimens   were   dredged   off  the    Californian  coast  by  the    U.    S.   Fish  Commission 
steamer  Albatross,  in  water  of  about  300  fathoms.     Figures  are  of  nearly  natural  size. 

Fig.  51. — Newly  hatched  young.     Length  about  10  cm.     This  shows  especially  the  great  width  of 
the  pectoral  fin,  the  relatively  large  eye,  and  the  lack  of  lateral  coloration. 

Fig.  51  a. — Dorsal  aspect  of  foregoing  specimen.      Observe  particularly  the  large  size  of  the  open- 
ings of  the  auditory  organ,  au. 

Fig.  51  b. — The  ventral  aspect  of  foregoing  specimen.     At  y.  s.  is  shown  the  scar,   marking  the 
point  of  entrance  of  the  yolk-sac. 

Fig.  52. — Young  of  about  12.5  cm.     This  specimen  shows  a  marked  differentiation  of  the  dorsal 
fin,  also  noteworthy  changes  in  coloration. 

Fig.  52  a. — Dorsal  aspect  of  foregoing  specimen. 

Fig.  53. — Young,  18.5  cm.  in  length.     This  exhibits  an  extreme  degree  of   pigmentation. 

Fig.  53  a. — Dorsal  aspect  of  foregoing  specimen. 

Fig.  53  b. — Ventral  aspect  of  foregoing  specimen. 


192 


CHI  MAE RA 


PLAIT:  x. 


51 


51E 


53a 


Lith  Anstv.Werneri'Winler,  Frankfurt  a/M 


PLATE  XI 
IMMATURE  SPECIMEN  OF  CHIMERA  COLLIEI. 

This  was  drawn  from  a  freshly  taken  specimen  and  is  intended  to  represent  the  fish  in  its 
natural  colors  ;  it  does  not,  however,  give  an  adequate  idea  of  the  brilliantly  metallic  shades  of 
the  living  fish,  or  of  the  translucency  of  the  snout  region.  At  this  stage  the  fins  are  deeply  pig- 
mented.  Natural  size. 


194 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWEI 

LAKTH  SC1EI-  if 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


?  7  1989 


OF  CALIF., 


LD  21-50m-4,'63 
(D647l6lO)4^6 


General  Library 

Universiry  of  California 

Berkeley 


